Enhancing the Performance of Motive Power Lead-Acid Batteries by High Surface Area Carbon Black Additives

applied sciences

Article Enhancing the Performance of Motive Power Lead-Acid Batteries by High Surface Area Carbon Black Additives

Hai-Yan Hu 1, Ning Xie 2, Chen Wang 1, Fan Wu 1, Ming Pan 1, Hua-Fei Li 2, Ping Wu 1, Xiao-Di Wang 1, Zheling Zeng 1, Shuguang Deng 1,3, Marvin H. Wu 4, K. Vinodgopal 5,* and Gui-Ping Dai 1,*

1 Key Laboratory of Poyang Lake Environment and Resource Utilization, Ministry of Education, School of Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, Jiangxi, China; [email protected] (H.-Y.H.); [email protected] (C.W.); [email protected] (F.W.); [email protected] (M.P.); [email protected] (P.W.); [email protected] (X.-D.W.); [email protected] (Z.Z.); [email protected] (S.D.) 2 Institute for Advanced Study, Nanchang University, Nanchang 330031, Jiangxi, China; [email protected] (N.X.); hﬂ[email protected] (H.-F.L.) 3 School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287, USA 4 Department of Physics, North Carolina Central University, Durham, NC 27707, USA; [email protected] 5 Department of Chemistry and Biochemistry, North Carolina Central University, Durham, NC 27707, USA * Correspondence: [email protected] (K.V.); [email protected] or [email protected] (G.-P.D.)

Received: 7 December 2018; Accepted: 26 December 2018; Published: 7 January 2019

Abstract: The effects of carbon black speciﬁc surface area and morphology were investigated by characterizing four different carbon black additives and then evaluating the effect of adding them to the negative electrode of valve-regulated lead–acid batteries for electric bikes. Low-temperature performance, larger current discharge performance, charge acceptance, cycle life and water loss of the batteries with carbon black were studied. The results show that the addition of high-performance carbon black to the negative plate of lead–acid batteries has an important effect on the cycle performance at 100% depth-of-discharge conditions and the cycle life is 86.9% longer than that of the control batteries. The excellent performance of the batteries can be attributed to the high surface area carbon black effectively inhibiting the sulfation of the negative plate surface and improving the charge acceptance of the batteries.

Keywords: carbon black; nano-structure; valve-regulated lead–acid batteries; electric bikes; cycle life

1. Introduction The lead–acid battery has a history of over 150 years and has a dominant position in electrochemical power supplies due to its low price, easy availability of raw materials and its full reliability in use, which is suitable for a wide range of environmental temperatures [1–5]. In the past decade, the electric bike industry has been unprecedentedly prosperous and electric bikes (e-bikes) have been gaining increasing attention in China [6]. In 2017, the total output of e-bikes in China was 29.96 million and the social ownership of e-bikes reached 250 million. However, poor cycle performance restricts the service life of valve-regulated lead−acid (VRLA) batteries for e-bikes. The e-bike batteries operate in the deep cycle duty and experience short charge and discharge pulses with high currents. The irreversible lead sulfate crystals grow on the negative electrode and form a barrier layer on the surface of the electrode, which further impedes electrolyte transfer and the charging and discharging process of the battery [7–11].

Appl. Sci. 2019, 9, 186; doi:10.3390/app9010186 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 186 2 of 13

To suppress the sulfation phenomenon of the negative plate, many researchers have found that different carbon materials (such as graphite [12–15], carbon black [7,16,17], activated carbon [12,15], or graphene [18–20]) can be added to the negative active material (NAM). The addition of the carbon material can increase the speciﬁc surface area (SSA) and overall conductivity of the NAM [21,22], promote the uniform spread of the lead sulfate on the surface of the negative plate, store excess charge and build a conductive network between the lead sulfate particles [8,20]. The carbon material can effectively extend the cycle life of the battery by suppressing the growth of lead sulfate in negative plates, but the effect of extending the service life differs according to their SSA. Fernandez et al. [15] reported that the SSA of the carbon material to the NAM is an important factor that affects the electrochemical performance of negative plates. Moseley [23] found that carbon black with a higher SSA at a high-rate partial-state-of-charge (HRPSoC) was more conducive to prolonging the cycle life of hybrid electric vehicle (HEV) batteries than carbon black with a lower SSA. Zou et al. [7] pointed out that under HRPSoC conditions, the addition of 0.5 wt % carbon black to the NAM of HEV batteries increased the utilization of the active material and thus boosted the cycle life by more than 255.5% at 1 C rate discharge. Nakamura et al. [24] reported that adding a certain amount of carbon black to the NAM of HEV batteries operating in partial-state-of-charge (PSoC) conditions effectively suppressed the accumulation of PbSO4 and improved the cycle life performance due to the conductive network of carbon particles formed on the PbSO4 particles. However, most studies have added carbon black to the negative plate for VRLA batteries in HEV applications [7,23,24]. Therefore, it is quite advantageous to add high performance carbon black in the NAM to further improve the charge acceptance and deep-cycling performance of batteries for e-bike applications. In the present work, we report, that high performance carbon black as a negative additive can signiﬁcantly increase the performance of e-bike VRLA batteries. When the batteries are cycled at a C2 rate discharge under a 100% depth-of-discharge (100% DoD) condition, the cycle life of the batteries with a higher SSA of carbon black is prolonged by more than 86.9% compared to that of the control batteries with acetylene black. Moreover, both the charge acceptance and larger current discharge performance of carbon black as a negative electrode additive are improved.

2. Experimental Methods

2.1. Carbon Black Materials In this experiment, three types of carbon black (provided by Cabot Company, Boston, MA, USA) were added to the negative plates. We studied the inﬂuence of three different SSAs of carbon black on the battery performance. Table1 summarizes the basic physical characteristics of the three kinds of carbon black additives.

Table 1. Characteristics of the carbon black additives used in this work. BET = Brunauer–Emmett– Teller method.

Negative Plate BET Surface (m2 g−1) Average Particle Size Symbol Additives of Additives (nm) of Additives Control batteries Acetylene black 20 45.0 CB1 batteries Carbon black 1 156 38.5 CB2 batteries Carbon black 2 234 25.6 CB3 batteries Carbon black 3 1378 4.3

2.2. Formation of VRLA Batteries E-bike batteries (48 V/12 Ah) (Figure 1) used in this study contain four 12 V modules interconnected in series to achieve 48 volts when the amp-hour capacity (12 Ah) remains the same. EachAppl. module Sci. 2019, (Figure9, 186 1b) consists of six 2-volt cells in series and each cell was prepared with four3 of 13 positive and five negative plates. Between each positive and negative plate was an absorbent glass matmat (AGM) (AGM) separator. separator. The The negative negative plate plate was was genera generallylly obtained obtained by by using using carbon carbon black black oror acetylene acetylene blackblack (control (control battery) battery) additives. additives. Based Based on on the the weig weightht of ofthe the leady leady oxide oxide powder powder (the (the oxidation oxidation degree degree ofof the the leady leady oxide oxide was was around around 76%), 76%), the the carbon carbon blac blackk and and acetylene acetylene black black additive additive content content of ofthe the the the NAMNAM was was 0.25 0.25 wt %.%. Meanwhile,Meanwhile, with with the the exception except ofion the of various the various carbon carbon blacks added,blacks alladded, conditions all conditionswere exactly were the exactly same asthe that same of a as regular that of commercial a regular manufacturingcommercial manufacturing process of e-bike process VRLA of batteries.e-bike VRLAManufacturing batteries. Manufacturing procedures included procedures lead oxide included power lead manufacturing, oxide power manufacturing, casting grids, slurry casting mixing grids, and slurrycoating, mixing plate and curing coating, and drying,plate curing formation and drying, of positive formation and negative of positive electrodes, and negative assembly electrodes, of batteries, assemblycasting andof batteries, welding, casting leak testing and welding, and acid leak (gel) testing ﬁlling. and acid (gel) filling.

Figure 1. (a) Group valve-regulated lead−acid (VRLA) (48 V 12 Ah) batteries contain four 12 V 12 Ah Figure 1. (a) Group valve-regulated lead−acid (VRLA) (48 V 12 Ah) batteries contain four 12 V 12 Ah modules and (b) schematic illustration showing a module consists of six 2-volt cells in series. modules and (b) schematic illustration showing a module consists of six 2-volt cells in series. 2.3. Battery Tests following China’s Standard e-Bike Test Profile 2.3. Battery Tests following China’s Standard e-Bike Test Profile 2.3.1. Capacity Test 2.3.1. Capacity Test Before a test can be performed, all test batteries need to be filled with charge. The fully charged batteriesBefore needa test to can be be cooled performed, for 4 h toall room test batteries temperature need before to be filled testing. with charge. The fully charged batteries need to be cooled for 4 h to room temperature before testing. Two-Hour Capacity Test Two-hourThe Capacity 2-h rate capacityTest test includes the following process: (i) the test batteries were placed in a ◦ ◦ constantThe 2-h temperature rate capacity box test of about includes 25 Cthe for following 12 h. When process: the temperature (i) the test ofbatteries the batteries were reachedplaced in 25 a C, constantthe 2-h temperature discharge capacity box of testabout was 25 conducted; °C for 12 h. (ii) When the batteries the temperature were discharged of the batteries at a constant reached current 25 °C,of the 6 A 2-h until discharge the voltage capacity decreased test was to 42 conducted; V and then (ii) the the batteries batteries were were continuously discharged recycled at a constant 3 times, currentrecording of 6 theA until third the discharge voltage time.decreased to 42 V and then the batteries were continuously recycled 3 times, recording the third discharge time. Low-Temperature Capacity Performance Tests (−10 ◦C and −15 ◦C) Low-TemperatureThere are two Capacity research Performance methods for Tests low-temperature (−10 °C and − performance:15 °C) one is charging at 25 ◦C and − ◦ − ◦ dischargingThere are attwo15 researchC. The methods fully charged for low-temperature batteries were placed performance: in a 15 oneC coldis charging box for at 12 25 h °C and and then dischargingdischarged at at − a15 6 °C. A fixed The fully current charged to 42 Vbatteries and the were measured placed discharge in a −15 °C time cold was box recorded. for 12 h Afterand then being dischargeddischarged, at thea 6 A batteries fixed current need to to be 42 fully V and charged the measured when they discharge return to time ambient was recorded. temperature. After The being other − ◦ discharged,research method the batteries involves need charging to be andfully discharging charged when at 10 theyC forreturn the wholeto ambient test process. temperature. The batteries The − ◦ otherwere research placed inmethod an environment involves charging at 10 C and for 12discharging h and then at the −10 batteries °C for the were whole fully test charged. process. After, The the batteriesbatteries were were placed discharged in an environment to 42 V at a fixed at −10 current °C for of12 6h Aand in athen low the temperature batteries were chamber. fully Thecharged. whole process was repeated five times and the duration of the fifth discharge was recorded.

Larger Current Discharge (1.8 C2) ◦ Batteries were placed in a temperature box of 25 C for 4 h, then discharged to 42 V with a 1.8 C2 rate and the discharge time was recorded. Appl. Sci. 2019, 9, 186 4 of 13

2.3.2. Charge Acceptance

The fully charged batteries were discharged at a current of I0 (I0 = Ca/10 A, where Ca (Ah) is the maximum value in the 2 h capacity test) for 5 h under ambient temperature conditions. Immediately after discharge, the batteries were placed in a 0 ◦C low temperature cabinet over 20 h. Then, the batteries were removed and charged at a 57.6 V constant voltage for 10 min and the current Ica was recorded. The charge acceptance ratio is Ica/I2 (I2 = C2/10 A, where C2 is the rated capacity of 2 h).

2.3.3. Cycling Performance Test under 100% DoD Condition The charge and discharge cycle processes of the test batteries were carried out as follows: (i) the fully charged batteries were discharged at a 6 A (C2 rate) constant current until the voltage decreased to 42 V at ambient temperature of about 25 ◦C; (ii) the batteries were charged at a constant current of 2.5 A to terminal voltage of 58.8 V, then they were charged at a 58.8 V constant voltage until the ﬁnal current of 0.5 A was reached before being rested for 10 min; (iii) the batteries continued charging with 55.2 V constant voltage for 4 h and then rested for 1 h; (iv) lastly, the batteries were exposed to the above charge/discharge cycle procedures until the two consecutive discharge times were below 93 min and the cycle life test was stopped.

2.4. Structural Characterization

The N2 adsorption/desorption isotherm and pore size distribution of carbon black additives were measured by using a Micromeritics ASAP 2460 instrument. The SSAs and pore volumes of the samples were acquired from the Brunauer–Emmett–Teller (BET) method. Pore size distribution was derived from the adsorption branch of the isotherms using the Barrett-Joyner-Halenda (BJH) model. Raman spectra of the samples were observed by a Lab RAM HR Evolution instrument using a 473 nm (blue) laser excitation. The FEI QUANTA 200F Scanning Electron Microscope (SEM) and the JEOL JEM-2100 Transmission Electron Microscope (TEM) were used to visualize the morphologies and microstructures of carbon black.

3. Results and Discussion

3.1. Morphology and Structure of Carbon Black Additives To derive the effect of different SSA carbon blacks on the performance of VRLA batteries, three kinds of carbon black materials were characterized by different physical properties (such as BET surface area, Raman, SEM and TEM). The SSA and pore volume of the carbon black additives were analyzed by using N2 adsorption/desorption isotherms, as shown in Figure2a. The isotherms of carbon black samples exhibit typical IV isotherms (The IV isotherm shows a significant inflection point in the lower region of the relative pressure (P/P0), and hysteresis loops occur under higher pressure due to the phenomenon of capillary condensation.) with a significant hysteresis loop, indicating the presence of a typical mesoporous structure in all samples [25]. The BET surface areas of carbon black 1 (CB1), CB2 and CB3 were 156 m2 g−1, 234 m2 g−1 and 1378 m2 g−1, with BJH adsorption cumulative volumes of pores of 0.387 cm3 g−1, 1.100 cm3 g−1 and 1.129 cm3 g−1, respectively. It is apparent that the CB3 sample possesses a larger surface area and a higher pore volume. Figure2b shows the pore size distribution of the three carbon black samples. There is only one mesopore peak in the curve of CB1 and CB3, which is mainly centered at 2.5 nm and 10 nm, respectively. However, the CB2 sample has two pore-size distribution peaks and the peaks of mesopore and macropore were about 2.5 nm and 50 nm, respectively. Carbon black with suitable mesopore distribution facilitates rapid diffusion of the acid electrolyte and promotes ion diffusion during the electrochemical processes [26]. Therefore, the mesoporous structure is conducive to improving the charge acceptance of VRLA batteries for e-bikes in the deep cycle duty. Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 13

size distribution peaks and the peaks of mesopore and macropore were about 2.5 nm and 50 nm, respectively. Carbon black with suitable mesopore distribution facilitates rapid diffusion of the acid electrolyte and promotes ion diffusion during the electrochemical processes [26]. Therefore, the mesoporous structure is conducive to improving the charge acceptance of VRLA batteries for e-bikes in the deep cycle duty. As seen in Figure 2c, the Raman spectra of carbon black exhibits two main characteristic peaks: the D band (1350 cm−1) is known as the disordered band and is caused by defects in the lattice of carbon atom, and the G band (1568 cm−1) reflects the crystalline and graphitic structure of the carbon materials [27]. The structural defects and the indication of disorder of the carbon black material can be characterized by the intensity ratio of ID/IG [28]. ID/IG is the ratio of the intensity of the D peak to that of the G peak. This ratio generally indicates the degree of defect density of the carbon material, and the larger the ratio of ID/IG, the greater the degree of defect of the material. Therefore, in the Raman spectra, the ID/IG values of CB1, CB2 and CB3 are calculated to be 0.80, 0.89 and 0.95, respectively, indicating that the CB3 sample has more defective sites. Accordingly, with the increase of SSA and pore volume, the defect degree of the samples is also increased. Meanwhile, the ratio of Appl. Sci. 2019, 9, 186 5 of 13 ID/IG is inversely proportional to the grain size, which is confirmed by TEM observations.

FigureFigure 2. 2.(a )(a Nitrogen) Nitrogen adsorption/desorption adsorption/desorption isotherms isotherms at at standard standard temperature temperature and and pressure pressure (STP), (STP), (b)(b Barrett-Joyner-Halenda) Barrett-Joyner-Halenda (BJH) (BJH) model model pore pore size distribution,size distribution, dV/dw dV/dw refers refers to the to change the change rate of porerate of

volumepore volume with pore with size. pore (c )size. Raman (c) Raman spectra spectra of carbon of carbon black 1 black (CB1), 1 (CB1), CB2 and CB2 CB3, and ID CB3,/IG isID/I theG is ratio the ratio of theof intensity the intensity of D peakof D peak to that to ofthat G peak.of G peak.

As seen in Figure2c, the Raman spectra of carbon black exhibits two main characteristic peaks: The morphology and microstructure of three samples with different SSAs of carbon black is the D band (1350 cm−1) is known as the disordered band and is caused by defects in the lattice of studied by SEM, TEM and high-resolution TEM (HRTEM), as shown in Figure 3. From the SEM carbon atom, and the G band (1568 cm−1) reflects the crystalline and graphitic structure of the carbon images, it can be seen that the CB1 (Figure 3a), CB2 (Figure 3b) and CB3 (Figure 3c) particles have a materials [27]. The structural defects and the indication of disorder of the carbon black material can be spherical structure. The mean size of CB1 particles is about 38 nm and they exhibited a certain degree characterizedof agglomeration. by the intensityThe average ratio particle of ID/I Gsize[28 ].of ICB3D/IG (aboutis the ratio4 nm) of is the significantly intensity of smaller the D peak than to that that of of the G peak. This ratio generally indicates the degree of defect density of the carbon material, and the larger the ratio of ID/IG, the greater the degree of defect of the material. Therefore, in the Raman spectra, the ID/IG values of CB1, CB2 and CB3 are calculated to be 0.80, 0.89 and 0.95, respectively, indicating that the CB3 sample has more defective sites. Accordingly, with the increase of SSA and pore volume, the defect degree of the samples is also increased. Meanwhile, the ratio of ID/IG is inversely proportional to the grain size, which is confirmed by TEM observations. The morphology and microstructure of three samples with different SSAs of carbon black is studied by SEM, TEM and high-resolution TEM (HRTEM), as shown in Figure3. From the SEM images, it can be seen that the CB1 (Figure3a), CB2 (Figure3b) and CB3 (Figure3c) particles have a spherical structure. The mean size of CB1 particles is about 38 nm and they exhibited a certain degree of agglomeration. The average particle size of CB3 (about 4 nm) is significantly smaller than that of CB2 (about 25 nm) and the aggregation of the small particles of CB3 is more severe than CB2. Furthermore, the CB1 particle size is obviously larger than that of the other two particles. As the particle size decreases, the SSA of carbon black increases. Figure3d–g further verify that CB1, CB2 and CB3 particles are irregular spherical structures whose particle size is basically consistent with the structure range obtained from the SEM images. At the same time, it can be seen by the HRTEM Appl. Sci. 2019, 9, x FOR PEER REVIEW 6 of 13

CB2 (about 25 nm) and the aggregation of the small particles of CB3 is more severe than CB2. Furthermore, the CB1 particle size is obviously larger than that of the other two particles. As the

Appl.particle Sci. 2019size, 9decreases,, 186 the SSA of carbon black increases. Figures 3d–g further verify that CB1,6 CB2 of 13 and CB3 particles are irregular spherical structures whose particle size is basically consistent with the structure range obtained from the SEM images. At the same time, it can be seen by the HRTEM (Figure(Figures3 h–j)3h–j) images images that that the the graphite graphite layer layer inside inside the the carbon carbon black black is is randomly randomly arranged, arranged,showing showing disorder phenomenon, indicating that carbon blackblack is anan amorphousamorphous structure.structure. The carbon black particles are connected to each otherother to form a network structure and the presence of pore structures in thesethese networknetwork structuresstructures isis mainlymainly derivedderived fromfrom unﬁlledunfilled voidsvoids betweenbetween thethe particles.particles. The pore structure of carbon black provides channels for the transmission of the acid electrolyte and facilitates the full contact between thethe electrolyteelectrolyte andand thethe surfacesurface ofof thethe negativenegative material.material.

Figure 3. (a–c) ScanningScanning electronelectron microscopymicroscopy (SEM) images, (e–g) transmissiontransmission electron microscopy (TEM) images,images, ((h–jj)) high-resolutionhigh-resolution TEMTEM (HRTEM)(HRTEM) imagesimages ofof CB1,CB1, CB2CB2 andand CB3,CB3, respectively.respectively.

3.2. Performance Tests ofof VRLAVRLA Batteries 3.2.1. Discharge Capacity Tests 3.2.1. Discharge Capacity Tests As shown in Figure4, VRLA batteries with different carbon black materials at 2-h rate, As shown in Figure 4, VRLA batteries with different carbon black materials at 2-h rate, low- low-temperature performance and 1.8 C2 discharge performance were compared to those of the temperature performance and 1.8 C2 discharge performance were compared to those of the control control batteries with acetylene black as a negative electrode additive. batteries with acetylene black as a negative electrode additive. Figure4a shows the 2-h rate capacity test of VRLA batteries. As can be seen in the figure, the Figure 4a shows the 2-h rate capacity test of VRLA batteries. As can be seen in the figure, the discharge times of CB1, CB2, CB3 and the control batteries at room temperature are 126 min, 127 min, discharge times of CB1, CB2, CB3 and the control batteries at room temperature are 126 min, 127 min, 128 min and 125 min, respectively. When CB3 is added as a negative electrode additive, the discharge 128 min and 125 min, respectively. When CB3 is added as a negative electrode additive, the discharge capacity of the batteries is highest and the discharge time is 128 min, which is 2.4% higher than that capacity of the batteries is highest and the discharge time is 128 min, which is 2.4% higher than that of the control batteries. Experimental results show that with the increase of SSA of carbon black, the of the control batteries. Experimental results show that with the increase of SSA of carbon black, the discharge capacity of the batteries is also increased. discharge capacity of the batteries is also increased. A battery’s low-temperature capacity is related to temperature. If the battery’s discharge capacity A battery’s low-temperature capacity is related to temperature. If the battery’s discharge is lower than the standard value (85 min) at low temperatures, the battery efficiency will decrease capacity is lower than the standard value (85 min) at low temperatures, the battery efficiency will under cold conditions, especially in northern China. In this paper, there are two research methods for decrease under cold conditions, especially in northern China. In this paper, there are two research low-temperature performance: one is charging at 25 ◦C and discharging at −15 ◦C, and the other is methods for low-temperature performance: one is charging at 25 °C and discharging at −15 °C, and charging and discharging at −10 ◦C. Figure4b shows a significant improvement of the discharge time the other is charging and discharging at −10 °C. Figure 4b shows a significant improvement of the of the batteries containing carbon black at a low temperature of −15 ◦C. The discharge times of CB1, CB2, CB3 and the control batteries are 103 min, 105 min, 110 min and 100 min, respectively. It can be found that the discharge time of the batteries with carbon black has a marginal improvement of 3–10% Appl. Sci. 2019, 9, x FOR PEER REVIEW 7 of 13 discharge time of the batteries containing carbon black at a low temperature of −15 °C. The discharge times of CB1, CB2, CB3 and the control batteries are 103 min, 105 min, 110 min and 100 min, respectively. It can be found that the discharge time of the batteries with carbon black has a marginal improvement of 3–10% compared to the control batteries [29]. The low temperature −10 °C performance test is shown in Figure 4c. These data indicate that batteries with carbon black additives have a significant improvement of 2–5% when compared to the control batteries. The results of the low-temperature discharge test at −15 °C and −10 °C indicate that carbon black as negative additives have better low-temperature performance and have a longer lifetime in low-temperature environments. In addition, CB3 has better low-temperature performance, which is due to the larger SSA of the CB3 additive, which can better improve the migration rate of ions [30]. Appl.E Sci.-bikes2019, 9have, 186 a large current discharge when they start, which has a great impact on the life7 of of 13 the batteries. It is observed from Figure 4d that the discharge time of the batteries with carbon black is slightly better than the control batteries at 1.8 C2 rate discharge. Compared with the C2 rate compared to the control batteries [29]. The low temperature −10 ◦C performance test is shown in discharge at 25 °C, the discharge capacity of the large current discharge is significantly decreased. Figure4c. These data indicate that batteries with carbon black additives have a significant improvement This is probably because the reaction occurs only on the surface of the active material on the negative of 2–5% when compared to the control batteries. The results of the low-temperature discharge test plate when a large current is discharged. PbSO4 crystals form an irreversible PbSO4 layer on the at −15 ◦C and −10 ◦C indicate that carbon black as negative additives have better low-temperature surface of the negative plate, which further impedes the HSO4− ions into the interior of the plate and performance and have a longer lifetime in low-temperature environments. In addition, CB3 has better reduces the reversible electrochemical reaction, which leads to the premature reduction of the low-temperature performance, which is due to the larger SSA of the CB3 additive, which can better battery’s capacity [31]. improve the migration rate of ions [30].

Figure 4. (a) Two-hour capacity tests at room temperature, (b,c) low-temperature performance tests at Figure 4. (a) Two-hour capacity tests at room temperature, (b,c) low-temperature performance tests −15 ◦C and −10 ◦C of VRLA (48 V 12 Ah) batteries with carbon black additives with different SSAs, at −15 °C and −10 °C of VRLA (48 V 12 Ah) batteries with carbon black additives with different SSAs, respectively. (d) Effect of carbon black on high-current discharge performance. (e) Effect of carbon respectively. (d) Effect of carbon black on high-current discharge performance. (e) Effect of carbon black on charge acceptance performance. black on charge acceptance performance. E-bikes have a large current discharge when they start, which has a great impact on the life 3.2.2. Charge Acceptance of the batteries. It is observed from Figure4d that the discharge time of the batteries with carbon blackThe is slightlycharge betteracceptance than thecapability control of batteries VRLA batteries at 1.8 C2 rateis an discharge. important Compared performance with metric the C for2 rate e- bikedischarge applications. at 25 ◦C, It thenot discharge only represents capacity the of recharge the large ability current of discharge the batter isies signiﬁcantly, but also objectively decreased. reflectsThis is probablythe service because life of thethe reactionbatteries occurs. The charge only on acceptance the surface ratio of the (Ica active/I2) of materialbatteries on with the different negative additivesplate when is shown a large in current Figure is4e. discharged. A higher charge PbSO acceptance4 crystals ratio form demonstrate an irreversibles that PbSO the batter4 layeries on ha theve − bettersurface charge of the negativeacceptance plate, [32 which]. The furtherbatteries impedes exhibit the better HSO 4chargeions intoacceptance the interior and of the their plate current and acceptancereduces the is reversible better. At electrochemical the same time, reaction,the polarization which leads of the to batteries the premature is not reductioneasy to achieve of the, battery’sthereby prolongingcapacity [31 the]. cycle life of the batteries. The Ica/I2 value of CB1, CB2, CB3 and the control batteries

3.2.2. Charge Acceptance The charge acceptance capability of VRLA batteries is an important performance metric for e-bike applications. It not only represents the recharge ability of the batteries, but also objectively reﬂects the service life of the batteries. The charge acceptance ratio (Ica/I2) of batteries with different additives is shown in Figure4e. A higher charge acceptance ratio demonstrates that the batteries have better charge acceptance [32]. The batteries exhibit better charge acceptance and their current acceptance is better. At the same time, the polarization of the batteries is not easy to achieve, thereby prolonging the cycle life of the batteries. The Ica/I2 value of CB1, CB2, CB3 and the control batteries are 3.8, 3.9, 4.5 and 2.9, respectively. Compared with the control batteries, the increase ranges between 30% and 55% with carbon black batteries. Furthermore, the charge acceptance ratio of batteries containing Appl. Sci. 2019, 9, x FOR PEER REVIEW 8 of 13

Appl.are 3.8, Sci. 3.9,2019 4.5, 9, 186and 2.9, respectively. Compared with the control batteries, the increase ranges between8 of 13 30% and 55% with carbon black batteries. Furthermore, the charge acceptance ratio of batteries containing high-SSA carbon black is superior to that of those containing low-SSA carbon black. These high-SSA carbon black is superior to that of those containing low-SSA carbon black. These results results clearly show the strong effect of the SSA of the carbon additive. The CB3 additive has a large clearly show the strong effect of the SSA of the carbon additive. The CB3 additive has a large SSA and SSA and the particles are interconnected to form a three-dimensional (3D) network structure, which the particles are interconnected to form a three-dimensional (3D) network structure, which provides a provides a larger active SSA for the crystallization and dissolution of lead sulfate particles, thus larger active SSA for the crystallization and dissolution of lead sulfate particles, thus improving the improving the charge acceptance of the batteries [32,33]. charge acceptance of the batteries [32,33].

3.2.3. Cycling Performance Charge andand discharge discharge cycle cycle life life is ais key a parameterkey parameter to measure to measure VRLA batteryVRLA performance.battery performance. Figure5 Figure 5 shows the dependence of the discharge time of four batteries on cycle number at C2 rate shows the dependence of the discharge time of four batteries on cycle number at C2 rate discharge dischargeunder 100% under DoD conditions.100% DoD Theconditions. actual discharge The actual capacity discharge of the capacity batteries wasof the the batteries discharge was current the dischargemultiplied current by the discharge multiplied duration. by the In discharge the initial duration. cycle, the capacityIn the initial of the cycle, batteries the increased capacity because of the batteriesof the activation increased process. because The of dischargethe activation capacity proces of thes. The control discharge batteries capacity was reduced of the control sharply batteries during was reduced sharply during the cycle and failed after only 225 cycles. From this figure, at C2 rate the cycle and failed after only 225 cycles. From this figure, at C2 rate discharge, the cycle numbers discharge,of the CB1, the CB2 cycle and numbers CB3 batteries of the wereCB1, 350,CB2 350and and CB3 430, batteries respectively, were 350, which 350 and are 52.2%,430, respectively, 52.2% and which86.9% higherare 52.2%, than 52.2% those and of the 86.9% controls, higher respectively, than those indicating of the cont thatrols, the respectively, addition of carbonindicating black that to the additionnegative plateof carbon of the black batteries to the can negative extend plate the cycle of th lifee batteries of the batteries. can extend Moreover, the cycle the life trend of the of batteries. CB1 and Moreover,CB2 batteries the showedtrend of noCB1 significant and CB2 differencebatteries showed under 100%no significant DoD test difference conditions. under CB3 100% batteries DoD have test conditions.longer cycle CB3 life batteries than CB1 have and CB2longer batteries, cycle life which than mayCB1 beand due CB2 to batteries, the uneven which dispersion may be of due CB1 to andthe unevenCB2 particles dispersion on the of plate CB1 [and34]. CB2 In addition, particles the on dischargethe plate [34]. time In of addition, the batteries the withdischarge CB3 heldtime steadyof the batteriesduring 300 with charge/discharge CB3 held steady cycles, during but 300 the charge discharge/discharge time decreased cycles, but rapidly the discharge after 300 time cycles, decreased possibly rapidlydue to the after stratification 300 cycles, ofpossibly electrolytes due to and the the stratificat excessiveionloss of electrolytes of water in and the electrolytesthe excessive [13 loss,35 ].of Aswater the in the electrolytes [13,35]. As the cycle number of the battery increases, a large amount of big and cycle number of the battery increases, a large amount of big and dense PbSO4 particles accumulate on densethe surface PbSO of4 particles the negative accumulate plate so on that the the surface Ohmic of the resistance negative of plate the batteries so that the continuously Ohmic resistance increases of theduring batteries the charge/discharge continuously increases process, during causing the the ch capacityarge/discharge to decline process, prematurely causing and the acceleratingcapacity to declinebattery failure.prematurely and accelerating battery failure.

Figure 5. 5. EffectEffect of ofcarbon carbon black black on the on cycle thecycle life of life VRLA of VRLA(48 V/12 (48 Ah) V/12 batteries Ah) batteriesunder 100% under depth-of- 100% depth-of-discharge (DoD) conditions at C discharge rate (6 A). Plots of the discharge time and the discharge (DoD) conditions at C2 discharge2 rate (6 A). Plots of the discharge time and the number of cyclesnumber for of three cycles different for three specific different surface speciﬁc areas surface (SSAs) areas of carbon (SSAs) black of carbon are used black as are negative used as additives negative foradditives lead–acid for lead–acidbatteries and batteries acetyl andene acetyleneblack as a blackcontrol as additive. a control additive. Based on the above results, it is possible to conclude that carbon black with high SSA has better Based on the above results, it is possible to conclude that carbon black with high SSA has better performance than carbon black with low SSA when added to the negative plate, which could effectively performance than carbon black with low SSA when added to the negative plate, which could inhibit the irreversible sulfation of VRLA batteries and prolong the cycle life [36]. In addition, the effectively inhibit the irreversible sulfation of VRLA batteries and prolong the cycle life [36]. In number of cycles of CB3 batteries increased by 86.9% compared to the control batteries at 100% DoD addition, the number of cycles of CB3 batteries increased by 86.9% compared to the control batteries conditions. These results can be attributed to the carbon black with greater SSA than acetylene black. at 100% DoD conditions. These results can be attributed to the carbon black with greater SSA than acetylene black. Appl. Sci. 2019, 9, x FOR PEER REVIEW 9 of 13 Appl. Sci. 2019, 9, 186 9 of 13 3.2.3. Water Loss Performance

3.2.4.During Water Loss the Performancecycle life of VRLA batteries for e-bikes, one of the main reasons for the failure of VRLA batteries is dry failure due to lack of water. The main reason for this is that the float charge voltageDuring is high, the cycle causing life ofthe VRLA battery batteries to lose for water e-bikes, faster, one ofso thethat main the reasonsbattery forcannot the failurework ofnormally VRLA batteriesbecause of is drythe excessive failure due polarization to lack of water.in the charging The main and reason discharging for this isprocess. that the At ﬂoat the end charge of charging, voltage isthe high, decomposition causing the of battery water toleads lose to water the separation faster, so of that hydrogen the battery and cannotoxygen; work this is normally the main becausefactor of ofwater the excessiveloss. The polarizationoxygen gas can in the perform charging the andoxygen discharging recombination process. reaction At the on end the of negative charging, plate, the decompositionwhile the hydrogen of water cannot leads be toabsorbed the separation and can ofonly hydrogen gather at and the oxygen;top of the this battery is the [1,37]. main When factor the of waterhydrogen loss. gas The reaches oxygen a gas certain can perform amount, the the oxygen safety recombinationvalve automatically reaction opens on the and negative releases plate, gas, whilecausing the water hydrogen loss. The cannot addition be absorbed of additives and to can the only negative gather active at the material top of thecan batteryimprove [1 the,37 ].battery’s When thecharge hydrogen acceptance gas reaches and low a certain temperature amount, performance. the safety valve However, automatically the presence opens andof some releases carbon gas, causingadditives water may loss. reduce The the addition hydrogen of additives evolution to over-pot the negativeential active of the material negative can electrode, improve leading the battery’s to an chargeincrease acceptance in the hydrogen and low evolution temperature of performance.the negative electrode. However, theCarbon presence black of as some an active carbon additive additives of maythe negative reduce the electrode hydrogen has evolution an important over-potential effect on water of the loss negative of the electrode, batteries. leading to an increase in the hydrogenThe water evolution loss of the of thefour negative batteries electrode. during the Carbon cycle is black shown as anin Figure active additive6. In the offigure, the negative with the electrodeincrease hasin cycle an important number, effectthe water on water loss lossof the of thecontrol batteries. batteries increased from 6.5 g to 17.1 g. In addition,The water the water loss loss of the of the four carbon batteries black during batteries the increased cycle is shown only slightly in Figure between6. In the 200 ﬁgure, cycles withof the thecontrol increase batteries, in cycle indicating number, that the the water water loss loss of the of the control batteries batteries containing increased carbon from black 6.5 g was to 17.1 within g. In a addition,controllable the waterrange lossand ofthere the was carbon no blackobvious batteries difference increased from onlythe control slightly batteries. between The 200 cycleswater loss of the of controlthe batteries batteries, with indicating carbon black that reached the water 30.8–31.2 loss of theg after batteries 350 cycles. containing Moreover, carbon the black CB3 wasbattery within water a controllableloss reached range 36.1 g and after there 400 wascycles. no The obvious water difference loss of the from battery the controlcan increase batteries. the acid The concentration, water loss of theaggravate batteries the with sulfation carbon degree black reached of the 30.8–31.2negative gpl afterate, magnify 350 cycles. the Moreover, internal resistance, the CB3 battery depress water the lossbattery reached capacity, 36.1 gshorten after 400 the cycles. battery The service water life loss and of even the battery lead to can the increasethermal therunaway acid concentration, of the battery aggravate[16,38]. the sulfation degree of the negative plate, magnify the internal resistance, depress the battery capacity, shorten the battery service life and even lead to the thermal runaway of the battery [16,38].

Figure 6. Diagram of the relationship between water loss and the number of cycles. Figure 6. Diagram of the relationship between water loss and the number of cycles. 3.3. Mechanism of the Effect of Adding Carbon Black on the Negative Plate 3.3. Mechanism of the Effect of Adding Carbon Black on the Negative Plate Based on the above research results, a model that can extend the service life of the battery by addingBased carbon on blackthe above is proposed. research Thisresults, model a model can betterthat can explain extend the the surface service reaction life of ofthe the battery battery by negativeadding carbon plate when black theis proposed. batteries ofThis e-bikes model are can charged better andexplain discharged the surface in deep reaction cycle of duty the battery under 100%negative DoD plate conditions. when the During batteries charging, of e-bikes small leadare charged sulfate crystals and discharged with high in solubility deep cycle can duty be reduced under to100% lead. DoD The largeconditions. PbSO4 Duringcrystals char withging, poor small solubility lead can sulfate hardly crystals be reduced with andhigh recrystallized solubility can into be largerreduced lead to sulfate lead. particles The large on thePbSO surface4 crystals of the negativewith poor plates solubilit [7,32,y39 ].can As hardly is well known,be reduced acetylene and blackrecrystallized and carbon into black larger are lead small sulfate spherical particles structures. on the Whensurface acetylene of the negative black (Figure plates7 a)[7,32,39]. and carbon As is blackwell known, (Figure 7acetyleneb) are added black as and negative carbon additives, black are point-to-pointsmall spherical contactstructures will. When be formed acetylene between black Appl. Sci. 2019, 9, x FOR PEER REVIEW 10 of 13

(Figure 7a) and carbon black (Figure 7b) are added as negative additives, point-to-point contact will be formed between carbon particles and PbSO4 particles and acetylene black particles may be independently dispersed on the negative plate to form conductive channels. For carbon black, the main factor influencing the conductive properties of carbon black is its structure, such as the degree of branching of carbon black. High-structure carbon black has a more developed chain structure than aggregates of low structural carbon black. It is possible that carbon black particles with high SSA are in contact with each other to form a continuous bead-like conductive network structure, while the low SSA carbon black forms a discontinuous chain structure due to the larger particle size. The less contact sides the carbon particles have between each other, the worse the charge transport and the electrical conductivity, so high SSA carbon black is more favorable for the diffusion of the electrolyte from the surface to the inside of the plate and the formation of small-sized lead sulfate crystals with high solubility [23,40]. Therefore, the high SSA carbon black additive can better inhibit the growth of the lead sulfate crystal on the negative plate and prolong the cycle life of the battery. Pavlov [41] proposed a model for the parallel mechanism of charge in which the electrochemical Appl. Sci. 2019, 9, 186 10 of 13 reaction process of the lead negative electrode occurs on both the surface of Pb and carbon black particles during the cycling of batteries under 100% DoD conditions. The electron migration diagram carbonof Pb and particles carbon and interface PbSO4 particlesin negative and plates acetylene is presented black particles in Figure may 7c. be independentlyWith the progress dispersed of the onreaction, the negative the PbSO plate4 crystals to form grow conductive continuously channels. to form For carbon a rough black, and thedense main irreversible factor inﬂuencing PbSO4 layer the conductiveon the surface properties of Pb ofand carbon the barrier black islayer its structure, of PbSO such4 not asonly the hinders degree of the branching ion migration, of carbon but black. also High-structureamplifies the charge carbon transfer black hasresistance a more (R developed1) at the interface chain structure of Pb/H than2SO4 aggregates[15,41]. However, of low structuralthe PbSO4 carbonbarrier black.layer Itis isnot possible formed that at carbon the C/H black2SO particles4 interface with because high SSA the aremesopores in contact of with carbon each material other to formconstruct a continuous the channel bead-like of ion diffusion conductive and network migration, structure, thus the while resistance the low (R2) SSA of carbonions passing black through forms a discontinuousthe C/H2SO4 interface chain structure is much due smaller to the than larger that particle of R1. Although size. The lessCB1, contact CB2 and sides CB3 the batteries carbon particleshave the havesamebetween proportion each of other, carbon the black, worse CB3 the chargebatteries transport have carbon and the black electrical that is conductivity, evenly dispersed so high on SSA the carbonnegative black electrode is more surface favorable compared for the diffusionto the other of the two electrolyte types of from batteries the surface and its to theeffect inside as an of theion platetransport and thechannel formation is greatly of small-sized increased. leadAs the sulfate particle crystals size of with CB3 high is smaller solubility than [23 that,40 ].ofTherefore, CB1 and CB2, the highit is easily SSA carbon dispersed black well additive among can the better active inhibit mate therial. growth Correspondingly, of the lead sulfate the batteries crystal oncontaining the negative CB3 platehave andexcellent prolong high-rate the cycle charge life of and the discharge battery. performance.

Figure 7. (a,b) Schematic diagram of acetylene black and carbon black on the negative plate under 100% DoD conditions, respectively. (c) Schematic diagram of ion migration through the Pb and carbon

interfaces in the negative plate. (R1 and IPb are the resistance and current of ions passing through the interface of Pb/H2SO4, respectively. R2 and IC are the resistance and current of ions passing through the interface of C/H2SO4, respectively.)

Pavlov [41] proposed a model for the parallel mechanism of charge in which the electrochemical reaction process of the lead negative electrode occurs on both the surface of Pb and carbon black particles during the cycling of batteries under 100% DoD conditions. The electron migration diagram of Pb and carbon interface in negative plates is presented in Figure7c. With the progress of the reaction, the PbSO4 crystals grow continuously to form a rough and dense irreversible PbSO4 layer on the surface of Pb and the barrier layer of PbSO4 not only hinders the ion migration, but also ampliﬁes the charge transfer resistance (R1) at the interface of Pb/H2SO4 [15,41]. However, the PbSO4 barrier layer is not formed at the C/H2SO4 interface because the mesopores of carbon material construct the channel of ion diffusion and migration, thus the resistance (R2) of ions passing through the C/H2SO4 interface Appl. Sci. 2019, 9, 186 11 of 13

is much smaller than that of R1. Although CB1, CB2 and CB3 batteries have the same proportion of carbon black, CB3 batteries have carbon black that is evenly dispersed on the negative electrode surface compared to the other two types of batteries and its effect as an ion transport channel is greatly increased. As the particle size of CB3 is smaller than that of CB1 and CB2, it is easily dispersed well among the active material. Correspondingly, the batteries containing CB3 have excellent high-rate charge and discharge performance.

4. Conclusions In this study, carbon black with different SSAs was used as the negative electrode additive of power VRLA batteries for e-bikes. The low-temperature performance, charge acceptance, larger current discharge performance and cycle life of VRLA batteries were investigated. The results show that compared with the control batteries containing acetylene black, adding carbon black additives to the batteries can signiﬁcantly enhance the low-temperature performance, improve the charge acceptance and prolong cycle life at 100% DoD conditions. The cycle life of batteries with carbon black increased from 225 to 430 times under 100% DoD conditions, which is 86.9% higher than that of the control batteries. Furthermore, the water loss of carbon black batteries was not signiﬁcantly different from that of control batteries. In addition, CB3 batteries had the most stable cycle performance and more remarkable charge acceptance stability, which is due to the larger SSA and pore volume of CB3. A larger SSA enlarges the electrochemical active surface of the active material and the smaller particle size carbon black is more easily dispersed within the active material. Carbon black has a rich mesoporous structure. Adding carbon black to the negative plate can effectively construct the internal and external transmission channels of the plate, increase the migration rate of ions, effectively alleviate the generation of negative plate sulfation and improve the battery’s charging acceptance performance and cycle life.

Author Contributions: G.-P.D. conceived and designed the experiments; H.-Y.H. performed the experiments; X.N., C.W., F.W., H.-F.L., M.P., P.W., X.D.W., Z.-L.Z., S.D., K.V., and G.-P.D. analyzed the data; M.H.W. contributed reagents/materials/analysis tools; H.-Y.H., K.V., and G.-P.D. wrote the paper. Funding: This research was funded by National Natural Science Foundation of China (Grants 51462022 and 51762032) and the Natural Science Foundation Major Project of Jiangxi Province of China (Grant 20152ACB20012) and NSF PREM (Award DMR 1523617). Acknowledgments: G.-P.D. acknowledges the National Natural Science Foundation of China (Grants 51462022 and 51762032) and the Natural Science Foundation Major Project of Jiangxi Province of China (Grant 20152ACB20012) for financial support of this research. K.V. and M.H.W. acknowledge the support of NSF PREM Award DMR 1523617. The assistance of Zhi-Qun Tian (HRTEM measurements) at Guangxi University and A.S. Kumbhar (SEM and HRTEM measurements), CHANL at UNC Chapel Hill, is also greatly appreciated. Conflicts of Interest: The authors declare no conflicts of interest.

References

1. Yang, J.; Hu, C.; Wang, H.; Yang, K.; Liu, J.B. Review on the research of failure modes and mechanism for lead-acid batteries: Reviews on the research of failure modes for lead-acid batteries. Int. J. Energy Res. 2017, 41, 336–352. [CrossRef] 2. Lam, L.T.; Newnham, R.H.; Ozgun, H.; Fleming, F.A. Advanced design of valve-regulated lead–acid battery for hybrid electric vehicles. J. Power Sources 2000, 88, 92–97. [CrossRef] 3. Zheng, S.; Jia, G.; Xue, W.; Huang, B. Performance of a lead–carbon negative electrode based on a Pb–C electrodeposited porous graphite/Pb conductive net skeleton. Micro Nano Lett. 2016, 11, 264–268. [CrossRef] 4. Huang, T.; Ou, W.; Feng, B.; Huang, B.; Liu, M.; Zhao, W.; Guo, Y. Researches on current distribution and plate conductivity of valve-regulated lead-acid batteries. J. Power Sources 2012, 210, 7–14. [CrossRef] 5. Enos, D.G.; Ferreira, S.R.; Barkholtz, H.M.; Baca, W.; Fenstermacher, S. Understanding Function and Performance of Carbon Additives in Lead-Acid Batteries. J. Electrochem. Soc. 2017, 164, A3276–A3284. [CrossRef] Appl. Sci. 2019, 9, 186 12 of 13

6. Muetze, A.; Tan, Y.C. Electric bicycles—A performance evaluation. Ind. Appl. Mag. IEEE 2007, 13, 12–21. [CrossRef] 7. Zou, X.; Kang, Z.; Dong, S.; Liao, Y.; Gong, Y.; He, C.; Hao, J.; Zhong, Y. Effects of carbon additives on the performance of negative electrode of lead-carbon battery. Electrochim. Acta 2015, 151, 89–98. [CrossRef] 8. Pavlov, D.; Nikolov, P.; Rogachev, T. Inﬂuence of carbons on the structure of the negative active material of lead-acid batteries and on battery performance. J. Power Sources 2011, 196, 5155–5167. [CrossRef] 9. Marom, R.; Ziv, B.; Banerjee, A.; Cahana, B.; Luski, S.; Aurbach, D. Enhanced performance of starter lighting ignition type lead-acid batteries with carbon nanotubes as an additive to the active mass. J. Power Sources 2015, 296, 78–85. [CrossRef] 10. Guo, Y.; Tang, S.; Meng, G.; Yang, S. Failure modes of valve-regulated lead-acid batteries for electric bicycle applications in deep discharge. J. Power Sources 2009, 191, 127–133. [CrossRef] 11. Lam, L.T.; Haigh, N.P.; Phyland, C.G.; Urban, A.J. Failure mode of valve-regulated lead-acid batteries under high-rate partial-state-of-charge operation. J. Power Sources 2004, 133, 126–134. [CrossRef] 12. Wang, L.Z.; Zhang, K.Q.; Zhang, L.S.; Zhang, Y.; Wang, K. Effect of carbon materials on electrochemical characteristics of negative electrodes of lead-acid battery. Chin. J. Power Sources 2012, 9, 22. [CrossRef] 13. Valenciano, J.; Sánchez, A.; Trinidad, F.; Hollenkamp, A.F. Graphite and ﬁberglass additives for improving high-rate partial-state-of-charge cycle life of valve-regulated lead-acid batteries. J. Power Sources 2006, 158, 851–863. [CrossRef] 14. Jaiswal, A.; Chalasani, S.C. The role of carbon in the negative plate of the lead–acid battery. J. Energy Storage 2015, 1, 15–21. [CrossRef] 15. Fernández, M.; Valenciano, J.; Trinidad, F.; Muñoz, N. The use of activated carbon and graphite for the development of lead-acid batteries for hybrid vehicle applications. J. Power Sources 2010, 195, 4458–4469. [CrossRef] 16. Pavlov, D.; Nikolov, P. Capacitive carbon and electrochemical lead electrode systems at the negative plates of lead–acid batteries and elementary processes on cycling. J. Power Sources 2013, 242, 380–399. [CrossRef] 17. Atanassova, P.; Blizanac, B.; Koehlert, K.C.; Moeser, G.D.; Oljaca, M.; Sun, Y.; Pierre, D.; Sawrey, J.S. Carbon Blacks and Use in Electrodes for Lead Acid Batteries. U.S. Patent 9,287,565[p], 15 March 2016. 18. Yeung, K.K.; Zhang, X.; Ciucci, F.; Yuen, M.M.F. Enhanced Cycle Life of a Lead-acid Battery Using Graphene as a Sulfation Suppression Additive in Negative Plates. RSC Adv. 2015, 5, 71314–71321. [CrossRef] 19. Li, X.; Zhang, Y.; Su, Z.; Zhao, Y.; Zhao, X.; Wang, R. Graphene nanosheets as backbones to build a 3D conductive network for negative active materials of lead–acid batteries. J. Appl. Electrochem. 2017, 47, 1–12. [CrossRef] 20. Long, Q.; Ma, G.; Xu, Q.; Ma, C.; Nan, J.; Li, A.; Chen, H. Improving the cycle life of lead-acid batteries using three-dimensional reduced graphene oxide under the high-rate partial-state-of-charge condition. J. Power Sources 2017, 343, 188–196. [CrossRef] 21. Nakamura, K.; Shiomi, M.; Takahashi, K.; Tsubota, M. Failure modes of valve-regulated lead/acid batteries. J. Power Sources 1996, 59, 153–157. [CrossRef] 22. Moseley, P.T.; Nelson, R.F.; Hollenkamp, A.F. The role of carbon in valve-regulated lead–acid battery technology. J. Power Sources 2006, 157, 3–10. [CrossRef] 23. Moseley, P.T. Consequences of including carbon in the negative plates of Valve-regulated Lead–Acid batteries exposed to high-rate partial-state-of-charge operation. J. Power Sources 2009, 191, 134–138. [CrossRef] 24. Shiomi, M.; Funato, T.; Nakamura, K.; Takahashi, K.; Tsubota, M. Effects of carbon in negative plates on cycle-life performance of valve-regulated lead-acid batteries. J. Power Sources 1997, 64, 147–152. [CrossRef] 25. Qin, C.; Ji, L.; Wu, K.; Zhang, W. Morphology-dependent Electrochemical Enhancements of Porous Carbon as Sensitive Determination Platform for Ascorbic Acid, Dopamine and Uric Acid. Sci Rep. 2016, 6, 22309.

26. Gai, Y.; Shang, Y.; Gong, L.; Su, L.; Hao, L.; Dong, F.; Li, J. A self-template synthesis of porous ZnCo2O4 microspheres for high-performance quasi-solid-state asymmetric supercapacitors. RSC Adv. 2017, 7, 1038–1044. [CrossRef]

27. Xia, J.; Zhang, L.; Fu, Y.; He, G.; Sun, X.; Wang, X. Nitrogen-doped carbon black supported NiCo2S4 catalyst for hydrogenation of nitrophenols under mild conditions. J. Mater. Sci. 2018, 53, 4467–4481. [CrossRef] 28. Gurunathan, S.; Han, J.W.; Kim, J.H. Green chemistry approach for the synthesis of biocompatible graphene. Int. J. Nanomed. 2013, 8, 2719–2732. [CrossRef] Appl. Sci. 2019, 9, 186 13 of 13

29. Swogger, S.W.; Everill, P.; Dubey, D.P.; Sugumaran, N. Discrete carbon nanotubes increase lead acid battery charge acceptance and performance. J. Power Sources 2014, 261, 55–63. [CrossRef] 30. Hong, B.; Jiang, L.; Xue, H.; Liu, F.; Jia, M.; Li, J.; Liu, Y. Characterization of nano-lead-doped active carbon and its application in lead-acid battery. J. Power Sources 2014, 270, 332–341. [CrossRef] 31. Lam, L.T.; Haigh, N.P.; Phyland, C.G.; Huynh, T.D. Novel technique to ensure battery reliability in 42-V PowerNets for new-generation automobiles. J. Power Sources 2005, 144, 552–559. [CrossRef] 32. Xiang, J.; Ding, P.; Zhang, H.; Wu, X.; Chen, J.; Yang, Y. Beneficial effects of activated carbon additives on the performance of negative lead-acid battery electrode for high-rate partial-state-of-charge operation. J. Power Sources 2013, 241, 150–158. [CrossRef] 33. Blecua, M.; Fatas, E.; Ocon, P.; Gonzalo, B.; Merino, C.; Fuente, F.D.L.; Valenciano, J.; Trinidad, F. Graphitized Carbon Nanofibers: New additive for the Negative Active Material of Lead Acid Batteries. Electrochim. Acta 2017, 257, 109–117. [CrossRef] 34. Ebner, E.; Burow, D.; Panke, J.; Börger, A.; Feldhoff, A.; Atanassova, P.; Valenciano, J.; Wark, M.; Rühl, E. Carbon blacks for lead-acid batteries in micro-hybrid applications—Studied by transmission electron microscopy and Raman spectroscopy. J. Power Sources 2013, 222, 554–560. [CrossRef] 35. Tantichanakul, T.; Chailapakul, O.; Tantavichet, N. Gelled electrolytes for use in absorptive glass mat valve-regulated lead-acid (AGM VRLA) batteries working under 100% depth of discharge conditions. J. Power Sources 2011, 196, 8764–8772. [CrossRef] 36. Wang, L.; Zhang, H.; Cao, G.; Zhang, W.; Zhao, H.; Yang, Y. Effect of activated carbon surface functional groups on nano-lead electrodeposition and hydrogen evolution and its applications in lead-carbon batteries. Electrochim. Acta 2015, 186, 654–663. [CrossRef] 37. Dietz, H.; Radwan, M.; Döring, H.; Wiesener, K. On the hydrogen balance in sealed lead/acid batteries and its effect on battery performance. J. Power Sources 1993, 42, 89–101. [CrossRef] 38. Bullock, K.R. Carbon reactions and effects on valve-regulated lead-acid (VRLA) battery cycle life in high-rate, partial state-of-charge cycling. J. Power Sources 2010, 195, 4513–4519. [CrossRef] 39. Calábek, M.; Micka, K.; Kˇrivák, P.; Baˇca,P. Significance of carbon additive in negative lead-acid battery electrodes. J. Power Sources 2006, 158, 864–867. [CrossRef] 40. Moseley, P.T.; Rand, D.A.J.; Peters, K. Enhancing the performance of lead–acid batteries with carbon—In pursuit of an understanding. J. Power Sources 2015, 295, 268–274. [CrossRef] 41. Pavlov, D.; Rogachev, T.; Nikolov, P.; Petkova, G. Mechanism of action of electrochemically active carbons on the processes that take place at the negative plates of lead-acid batteries. J. Power Source 2009, 191, 58–75. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).