Mastering the Interface for Advanced All-Solid-State Lithium Rechargeable Batteries

Mastering the interface for advanced all-solid-state lithium rechargeable batteries

Yutao Lia,b,1, Weidong Zhoua,b,1, Xi Chena,b,1, Xujie Lüc, Zhiming Cuia,b, Sen Xina,b, Leigang Xuea,b, Quanxi Jiac, and John B. Goodenougha,b,2

aMaterials Science and Engineering Program, The University of Texas at Austin, Austin, TX 78712; bTexas Materials Institute, The University of Texas at Austin, Austin, TX 78712; and cCenter for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545

Contributed by John B. Goodenough, September 30, 2016 (sent for review August 24, 2016; reviewed by Ken Poeppelmeier and Jean-Marie Tarascon) A solid electrolyte with a high Li-ion conductivity and a small The stability of the solid electrolyte on contact with a lithium interfacial resistance against a Li metal anode is a key component anode is a critical issue. If a lithium anode reduces the electro- in all-solid-state Li metal batteries, but there is no ceramic oxide lyte, (i) the electrolyte may become an electronic conductor, + electrolyte available for this application except the thin-film Li-P (ii) an interface layer may form that blocks Li transfer, or (iii)an + oxynitride electrolyte; ceramic electrolytes are either easily re- interface layer may form that conducts Li ions with a low im- duced by Li metal or penetrated by Li dendrites in a short time. pedance. The third situation forms with a LiZr2(PO4)3 electro- + Here, we introduce a solid electrolyte LiZr2(PO4)3 with rhombohe- lyte. In this paper, we report that a Li electrolyte with the dral structure at room temperature that has a bulk Li-ion conduc- NASICON structure, LiZr2(PO4)3, can be fabricated by using −4 −1 tivity σLi = 2 × 10 S·cm at 25 °C, a high electrochemical stability + + zirconium acetate as the precursor and spark plasma sintering up to 5.5 V versus Li /Li, and a small interfacial resistance for Li + + (SPS); it forms a stable Li -conducting SEI that is wet by a transfer. It reacts with a metallic lithium anode to form a Li -con- metallic lithium anode and also wets the electrolyte to provide a ducting passivation layer (solid-electrolyte interphase) containing safe, all-solid-state Li/LiFePO4 cell operating at Top = 80 °C with Li P and Li ZrO that is wet by the lithium anode and also wets the 3 8 6 a long cycle life; the LiFePO4 cathode particles are embedded in LiZr2(PO4)3 electrolyte. An all-solid-state Li/LiFePO4 cell with a polymer a polymer catholyte and carbon.

catholyte shows good cyclability and a long cycle life. CHEMISTRY Results and Discussion solid electrolyte | lithium anode | polymer catholyte | interfaces | NASICON The X-ray diffraction (XRD) results of as-prepared LiZr2(PO4)3 are shown in Fig. 1A; the phase of LiZr2(PO4)3 depended on the + rechargeable cell having a flammable organic liquid Li starting materials. Although different zirconium salts decomposed T < B Aelectrolyte has enabled the wireless revolution, but it is not at the same temperature 400 °C (Fig. 1 ), a pure LiZr2(PO4)3 able to power safely an electric road vehicle at a cost that is phase with rhombohedral structure could only be obtained with competitive with the gasoline-powered internal combustion en- zirconium acetate; a triclinic phase with space group C-1was gine (1–4). Safety concerns as well as cost, volumetric energy obtained with other zirconium materials. LiZr2(PO4)3 prepared by density, and cycle life have prevented realization of a commer- solid-state reaction with ZrO2 as the starting material was repor- cially viable electric road vehicle. To address this problem, ted to change from triclinic to rhombohedral structure at 60 °C considerable effort is being given to the development of a solid (13, 14). The rhombohedral LiZr2(PO4)3 phase with high Li-ion + + Li or Na electrolyte that is wet by a metallic lithium or sodium conductivity was stable at room temperature with zirconium ace- −4 −1 anode and has an alkali ion conductivity σi > 10 S·cm at the tate as the starting zirconium salt. The XRD refinement of the C cell operating temperature Top, where a Top ≤ 25 °C is desired rhombohedral LiZr2(PO4)3 phase is shown in Fig. 1 with re- (5–10). Such a development would allow new as well as tradi- liability factors (Rwp = 11.0%; RB = 2.3%). The rhombohedral tional strategies for the cathode. Wetting of the solid electrolyte surface is desired not only because it prevents dendrite forma- Significance tion and growth during plating of an alkali metal anode, but also because wetting constrains the anode volume change in a charge/ Realization of a safe, low-cost rechargeable lithium battery of discharge cycle to be perpendicular to the anode/electrolyte in- high energy density and long cycle life is needed for powering terface, thereby allowing a long cycle life. Therefore, the shear an electric road vehicle and for storing electric power gener- modulus of the electrolyte may not be critical where lithium wets ated by solar or wind energy. This urgent need has prompted the electrolyte surface. efforts to develop a solid electrolyte with an alkali metal an- Ceramic oxide electrolytes offer a large energy gap between ode. Only now is it recognized that the key requirement is their conduction and valence bands, which can allow realization wetting of the electrolyte surface by the alkali-metal anode. of a battery cell with a large energy separation between the an- We report a full rechargeable cell with a solid electrolyte that, ode and cathode chemical potentials without either reduction or although it is reduced by metallic lithium, forms a thin lithium– electrolyte interface that is wet by the anode and wets the oxidation of the electrolyte by an electrode (2). However, if an + alkali-metal anode reduces the solid electrolyte, formation of a electrolyte to give a small Li transfer resistance across the stable solid-electrolyte interphase (SEI) that conducts the working interface. + + + + Li or Na ion is acceptable if the Li or Na transfer across the SEI + Author contributions: Y.L. and J.B.G. designed research; Y.L., W.Z., X.C., Z.C., S.X., and L.X. has a low resistance. Although many ceramic solid Li electrolytes performed research; Y.L., W.Z., X.L., and Q.J. analyzed data; and Y.L. and J.B.G. wrote have been investigated, they are easily reduced by Li metal and/or the paper. they have failed to block dendrite formation and growth into their Reviewers: K.P., Northwestern University; and J.-M.T., Collège de France. grain boundaries (SI Appendix,Fig.S1). However, the rhombo- The authors declare no conflict of interest. hedral structure of the Na electrolyte Na1+3xZr2(SixP1–xO4)3 (11), 1Y.L., W.Z., and X.C. contributed equally to this work. NASICON, which was developed over 45 y ago, has recently been 2To whom correspondence should be addressed. Email: [email protected]. used in a cell design in which a seawater cathode provides the so- This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. dium of the anode (12). 1073/pnas.1615912113/-/DCSupplemental.

www.pnas.org/cgi/doi/10.1073/pnas.1615912113 PNAS Early Edition | 1of5 Downloaded by guest on October 1, 2021 Fig. 1. (A) XRD patterns of LiZr2(PO4)3 prepared with different starting materials. (B) Thermogravimetric analysis (TGA) curves of LiZr2(PO4)3 with different starting materials. (C) Rietveld analysis of the XRD data of rhombohedral LiZr2(PO4)3.(D) SEM image of rhombohedral LiZr2(PO4)3 prepared by SPS at 1,000 °C for 10 min.

phase has a space group R-3c with lattice parameters a = 8.8442 Å which is smaller than that (0.40 eV) of LiZr2(PO4)3 prepared by and c = 22.2645 Å, which is very close to those of LiZr2(PO4)3 at solid-state reaction (15, 16). In rhombohedral LiZr2(PO4)3 400 °C prepared by solid-sate reaction. A pure rhombohedral (Fig. 1C, Inset), 90% and 10% Li ions occupy, respectively, the LiZr2(PO4)3 phase was also obtained by SPS. The electron-dis- sixfold disordered 36f M1 sites and the threefold disordered 18e persive spectroscopy mapping in SI Appendix,Fig.S2indicates a M2 sites (13). The interstitial space is large enough for Li-ion uniform distributions of Zr, P, and O elements in the LiZr2(PO4)3 transport, and higher Li-ion conductivity may be obtained by pellet. The LiZr2(PO4)3 pellets fired at 1,150 °C for 20 h in a box doping with different valent ions to increase the Li-ion population furnace and fired at 1,000 °C for 100 min by SPS have a density of inside the framework. –3 –3 + 85% (2.66 g·cm , SI Appendix,Fig.S3) and 99.9% (3.15 g·cm , Whereas a garnet Li electrolyte can have a higher bulk σLi = −3 −1 Fig. 1D), respectively. 1 × 10 S·cm at 25 °C (17), an insulating Li2CO3 surface layer A pure rhombohedral LiZr2(PO4)3 phase can be obtained forms on exposure to moist air; the interfaces of a symmetric Li/ + + + as a well-sintered ceramic at 1,200 °C by Y3 or Ca2 doping for garnet/Li cell create a large resistance to Li transfer between + − Zr4 ; the rhombohedral structure remains unchanged from –70 °C the anode and the electrolyte (about 1,700 Ω·cm 2, SI Appendix, to 200 °C (15). The acetate route supplies particles with the Fig. S5) that dominates the total resistance of the electrolyte. rhombohedral phase in a single firing at 900 °C; it is a simpler route, In contrast, the SEI in the Li/LiZr2(PO4)3/Li interfaces with a but the product undergoes a reversible change from rhombohedral 400-μm-thick electrolyte pellet gave an interfacial resistance of − to triclinic symmetry on cooling through 15 °C (SI Appendix,Fig. 650 Ω·cm 2 at 80 °C in the absence of an applied pressure on the S3). Both products give comparable ionic conductivities at 80 °C. cell. The much lower interfacial resistance of the Li/LiZr2(PO4)3/Li + The impedance spectra of LiZr2(PO4)3 prepared with differ- cell makes LiZr2(PO4)3 a much better Li solid electrolyte ent starting materials are shown in Fig. 2 and SI Appendix, Fig. than garnet. S3. The rhombohedral LiZr2(PO4)3 pellets fired by conventional The electrochemical compatibility and stability of LiZr2(PO4)3 sintering in a box furnace and by SPS at 1,000 °C for 10 min have, with Li metal was evaluated further at 80 °C with symmetric Li/ −5 –1 respectively, Li-ion conductivities of 2.2 × 10 S·cm and 3.8 × LiZr2(PO4)3/Li cells by subjecting them to different current − – – – 10 5 S·cm 1 at 25 °C, which is two to three orders of magnitude densities from 50 μA·cm 2 to 350 μA·cm 2. The symmetric cell – higher than those of the room-temperature triclinic phases; the pellet showed good cyclability at current densities less than 200 μA·cm 2, − − – fired by SPS method has a Li-ion conductivity of 1.8 × 10 4 S·cm 1 but the current densities above 200 μA·cm 2 increased the voltage –2 at 80 °C. The bulk Li-ion conductivity of rhombohedral LiZr2(PO4)3, a little after 50 h. At 50 μA·cm , the symmetric cell has a low as calculated from the distance between the zero point and the left overpotential of about 0.13 V and there is no evident voltage in- −4 −1 interception of the semicircle with the Z′′ axis, was 2 × 10 S·cm crease after 120 h; the interface between Li metal and LiZr2(PO4)3 at 25 °C (SI Appendix,Fig.S3). The activation energy of is very stable. Li/ LiZr2(PO4)3/Li cells were tested at 80 °C for up rhombohedral LiZr2(PO4)3 calculated from an Arrhenius plot to 500 h. At 80 °C, a sealing problem with the coin cells resulted over 300 K to 450 K in SI Appendix,Fig.S4was 0.28 eV, in oxidation of the lithium, but there was no evidence of failure

2of5 | www.pnas.org/cgi/doi/10.1073/pnas.1615912113 Li et al. Downloaded by guest on October 1, 2021 spectrum corresponds to adventitious carbon, and the small peak at 286.2 eV in SI Appendix, Fig. S9 may be from the residue of the polymer glue during the polishing process. No Li2CO3 peak at 288 eV was observed; LiZr2(PO4)3 is more stable against moist air than garnet Li7La3Zr2O12, which forms a Li-ion insulating Li2CO3 layer on the particle surfaces during cooling in the firing process. The NASICON structure with strong P–O bonds usually has high stability against moist air; for example, NASICON Li1.3Al0.3Ti1.7(PO4)3 is stable in air and in water (18, 19). A Li2CO3-related peak in the C 1s spectrum was from the reaction 4+ of Li metal with organic electrolyte in the glove box. The Zr 3d3/2 and 3d5/2 peaks at 185.5 eV and 183.13 eV in LiZr2(PO4)3 shifted, respectively, to 184.8 eV and 181.7 eV after reaction, 4+ which is similar to the binding energy of Zr in ZrO2. After reaction, one more peak at 127.13 eV in the P 2p spectrum 3– corresponds to P ions in Li3P, and the peak at 132.8 eV is from 5+ 2– the P ions in LiZr2(PO4)3.TheO 2p peaks in LiZr2(PO4)3 shifted from 531.25 eV to 530.3 eV after reaction, which is the 2– same as the O 2p binding energy in Li8ZrO6.NoclearLi1s binding energy difference was observed in LiZr2(PO4)3 before and after reaction. Li3P in the thin layer is a good Li-ion conductor, and Li8ZrO6 with a layer structure may also have some Li-ion conductivity. After the reaction of LiZr2(PO4)3 with Li metal, a Li/LiZr2(PO4)3/Au cell was assembled with Au contacting the black thin layer; the cyclic voltammogam of the cell in SI Appendix,Fig.S10showed that the black thin layer was CHEMISTRY

Fig. 2. (A) The impedance plots of LiZr2(PO4)3 at 25 °C and 80 °C. (B)Theim- pedance plots Li/LiZr2(PO4)3/Li symmetric cell. (C) Cyclability of the Li/LiZr2(PO4)3/Li symmetric cell for 300 h with different current densities. (D) Surface SEM image

of a LiZr2(PO4)3 pellet after cycling the cell for 100 h. (E) SEM image of Li metal – after charging the symmetric cell for 20 h at 150 μA·cm 2.

by dendrite formation and growth. After cycling a Li/LiZr2(PO4)3/Li cell for 10 h, a thin layer with black color formed only on the surface of the LiZr2(PO4)3 pellet (SI Appendix,Fig.S6). No new diffraction peaks except those of the rhombohedral LiZr2 (PO4)3 were observed with this thin layer (SI Appendix,Fig.S7), and no Li dendrites were found on the LiZr2(PO4)3 pellet after cycling the symmetric cell at different current densities for 300 h. The Raman inactive spectra of the black thin layer in Fig. 3A indicated that the thin layer was amorphous. Fig. 2D shows the surface of LiZr2(PO4)3 after cycling the Li/LiZr2(PO4)3/Li cell at – 50 μA·cm 2 for100h;theparticlesizewasmuchsmallerthanthatof fresh LiZr2(PO4)3, but it still kept a dense surface structure. There were no Li metal dendrites on the Li metal surface after cycling the – symmetric cell at 150 μA·cm 2 for 20 h (Fig. 2E and SI Appendix, Fig. S8). The lithium metal wet well the surface of the thin surface layer on the LiZr2(PO4)3 electrolyte that formed on reaction with aLielectrode. To explore the composition of the thin interfacial layer that formed during cycling at 80 °C, a Li metal foil on the surface of a LiZr2(PO4)3 pellet was heated from 25 °C to 350 °C (SI Ap- pendix, Fig. S6). For temperature below 300 °C, there was no change of the LiZr2(PO4)3 pellet; a dense, black thin layer on the surface of LiZr2(PO4)3 was formed when the pellet was heated at 350 °C for 30 min. The XRD result of the pellet confirmed the decomposition of LiZr2(PO4)3 to trigonal Li8ZrO6 and hexago- nal Li3P phases by the reaction

24Li + LiZr2ðPO4Þ → 2Li8ZrO6 + 3Li3P. 3 Fig. 3. (A) Raman spectra of the black SEI layer on the surface of LiZr2(PO4)3 after cycling the Li/LiZr (PO ) /Li cell for 10 h. (B) XRD pattern of LiZr (PO ) C−F 2 4 3 2 4 3 The XPS result of the black thin layer is shown in Fig. 3 and after reaction with Li metal at 350 °C for 0.5 h. (C−F) XPS data of LiZr2(PO4)3 SI Appendix, Fig. S9; the main peak at 284.8 eV in the C 1s before and after reaction with Li metal at 350 °C for 0.5 h.

Li et al. PNAS Early Edition | 3of5 Downloaded by guest on October 1, 2021 –1 Fig. 4. (A) A cyclic voltammogram of LiZr2(PO4)3 at a scanning rate of 0.5 mV·s .(B) The impedance plots of all-solid-state Li/LiZr2(PO4)3/LiFePO4 cell. (C) Charge and discharge voltage profiles and (D) cycling performance of an Li/LiZr2(PO4)3/LiFePO4 all-solid-state battery at 80 °C with different current densities.

unstable at high voltage. The Li3P was reported to decompose 5.5 V. An all-solid-state Li metal battery with LiZr2(PO4)3 as a solid at voltage above 0.7 V, which resulted in a voltage increase in electrolyte contacting a Li metal anode showed no Li dendrite the Li/LiZr2(PO4)3/Li cell at high current densities. For the appli- formation and good cycling performance with a Li insertion cathode cation of LiZr2(PO4)3 in Li metal batteries, the thin layer only embedded in a polymer catholyte. forms at the Li metal side, so the electrolyte will be stable during the charge/discharge process of an all-solid-state Li metal battery. Materials and Methods The electrochemical stability window of LiZr2(PO4)3 is shown The stoichiometric amounts of Li2CO3,(NH4)2HPO4, and different zirconium + in Fig. 4A; the two peaks near 0 V versus Li /Li correspond to Li salts [Zr(AC)4, ZrOCl2, Zr(NO4)3 and ZrO2] were fired at 900 °C for 10 h, and metal deposition and dissolution; there were no other redox the obtained powders were ground and fired at 1,150 °C for 20 h in a Pt peaks up to 5.5 V. An all-solid-state Li/LiZr (PO ) /LiFePO crucible. The SPS pellets were obtained by firing the powders after 900 °C at 2 4 3 4 1,000 °C for 10 min with a pressure of 50 Mpa. Powder XRD was used to battery was fabricated with the LiFePO4 cathode embedded in a · –2 monitor the phase formation with a step size of 0.02°. A field emission Li-ion polymer electrolyte and carbon in a loading of 2 mg cm . scanning electron microscope was used to obtain the fracture surface mi- The polymer membrane with a melting point of 240 °C has a crostructure of the pellet, and the distribution of elements was measured by −4 −1 Li-ion conductivity of 1 × 10 S·cm and an electrochemical energy dispersive spectroscopy. Ionic conductivity was measured from 298 K stability up to 4.7 V at 65 °C. The Li/LiZr2(PO4)3/LiFePO4 to 450 K with a Solarton Impedance Analyzer. Cyclic voltammetry was carried · −1 battery had a small interfacial resistance with LiFePO4 of about outonanAutoLabworkstationatascanrateof0.5mVs .TheLi/LiZr2(PO4)3/Li −2 −2 300 Ω·cm and a total resistance of 1,100 Ω·cm at 80 °C symmetric cell was prepared by putting lithium foil on both sides of the LiZr2(PO4)3 (Fig. 4B), which is smaller than those of previously reported all- pellet, and the cell was cycled with different current densities in a Land in- solid-state batteries (20). Fig. 4C shows the charge/discharge strument. The LiFePO4 preparation process was the same as in our previous – – report (20). To prepare the cathode of an all-solid-state LiFePO /Li cell, the voltage profiles at current densities of 50 μA·cm 2,75μA·cm 2, 4 μ · –2 active material LiFePO4 was mixed with carbon black, cross-linked poly- and 100 A cm at 80 °C; the cells had a discharge capacity of ethylene oxide, and LiTFSI (60:12:20:8 by weight) and ground in a mortar. The · –1 · –1 140 mAh g and 120 mAh g with a cell polarization of 0.1 V mixture was then dispersed in dimethylfluoride and stirred overnight. The –2 –2 and 0.2 V at 50 μA·cm and 100 μA·cm , respectively. A high obtained slurry was spread evenly on a carbon-coated aluminum foil to pro- – coulombic efficiency of 99.5 ± 0.5% over 40 cycles was obtained, duce an electrode film with an active material loading of 2 mg·cm 2, which which indicates that the Li/LiZr2(PO4)3 and LiZr2(PO4)3/LiFePO4 was dried at 90 °C for 12 h under vacuum. Then, 2,032 coin cells were fabri- interfaces were stable during cycling. cated in an argon-filled glove box with lithium foil as the anode. The cell was tested between 2.7 V and 3.8 V vs. Li+/Li in a Land instrument. Conclusions ACKNOWLEDGMENTS. This work was supported by National Science Foun- We have prepared a stable rhombohedral NASICON LiZr2(PO4)3 dation (NSF) Grant CBET-1438007 and the US Department of Energy, Office electrolyte at room temperature. A thin amorphous interfacial layer of Basic Energy Sciences, Division of Materials Sciences and Engineering, containing Li8ZrO6 and Li3PformedontheLiZr2(PO4)3 surface by under Award DESC0005397. The SPS processing at The University of Texas at reaction with Li metal; this layer is wet by Li metal, which suppresses Austin was conducted with an instrument acquired with the support of NSF Award DMR-1229131. The work at Los Alamos National Laboratory was Li dendrite formation. LiZr2(PO4)3 has a Li-ion conductivity of 2 · −4 · −1 performed, in part, at the Center for Integrated Technologies, an Office of 10 S cm at 80 °C, a small interfacial resistance against Li metal Science User Facility operated for the US Department of Energy Office of and a LiFePO4 cathode, and a large electrochemical window up to Science.

4of5 | www.pnas.org/cgi/doi/10.1073/pnas.1615912113 Li et al. Downloaded by guest on October 1, 2021 1. Tarascon JM, Armand M (2001) Issues and challenges facing rechargeable lithium 12. Kim Y, Kim H, Park S, Seo I, Kim Y (2016) Na ion conducting ceramic as solid elec- batteries. Nature 414(6861):359–367. trolyte for rechargeable seawater batteries. Electrochim Acta 191:1–7.

2. Goodenough JB, Kim Y (2010) Challenges for rechargeable Li batteries. Chem Mater 13. Catti M, Comotti A, Di Blas S (2003) High-temperature lithium mobility in α-LiZr2(PO4)3 22(3):587–603. NASICON by neutron diffraction. Chem Mater 15(8):1628–1632. + 3. Goodenough JB, Park KS (2013) The Li-ion rechargeable battery: A perspective. JAm 14. Catti M, Morgante N, Ibberson RM (2000) Order–disorder and mobility of Li in the Chem Soc 135(4):1167–1176. β′-and β-LiZr2(PO4)3 ionic conductors: A neutron diffraction study. J Solid State Chem 4. Ellis BL, Lee KT, Nazar LF (2010) Positive electrode materials for Li-Ion and Li-batteries. 152(2):340–347. – + Chem Mater 22(3):691 714. 15. Li Y-T, Liu M-J, Liu K, Wang C-A (2013) High Li conduction in NASICON-type 5. Murugan R, Thangadurai V, Weppner W (2007) Fast lithium ion conduction in garnet- Li1+xYxZr2−x(PO4)3 at room temperature. J Power Sources 240:50–53. type Li7La3Zr2O12. Angew Chem Int Ed Engl 46(41):7778–7781. + 16. Xie H, Goodenough JB, Li Y-T (2011) Li1.2Zr1.9Ca0.1(PO4)3, a room-temperature Li-ion 6. Adachi GY, Imanaka N (1996) Aono H fast Li conducting ceramic electrolytes. Adv solid electrolyte. J Power Sources 196(18):7760–7762. Mater 8(2):127–135. + 17. Li Y-T, Han J-T, Wang C-A, Xie H, Goodenough JB (2012) Optimizing Li conductivity 7. Catti M (2007) First-principles modeling of lithium ordering in the LLTO (LixLa2/3-x/3TiO3) in a garnet framework. J Mater Chem 22(30):15357–15361. superionic conductor. Chem Mater 19(16):3963–3972. 18. Hasegawa S, et al. (2009) Study on lithium/air secondary batteries—Stability of 8. Thangadurai V, Narayanan S, Pinzaru D (2014) Garnet-type solid-state fast Li ion – conductors for Li batteries: Critical review. Chem Soc Rev 43(13):4714–4727. NASICON-type lithium ion conducting glass ceramics with water. J Power Sources 189(1):371–377. 9. Lü X, et al. (2014) Li-rich anti-perovskite Li3OCl films with enhanced ionic conductivity. — Chem Commun (Camb) 50(78):11520–11522. 19. Shimonishi Y, et al. (2011) A study on lithium/air secondary batteries Stability of the 10. Li Y, et al. (2016) Fluorine-doped antiperovskite electrolyte for all-solid-state lithium- NASICON-type lithium ion conducting solid electrolyte in alkaline aqueous solutions. ion batteries. Angew Chem Int Ed Engl 55(34):9965–9968. J Power Sources 196(11):5128–5132. + 11. Goodenough JB, Hong HYP, Kafalas JA (1976) Fast Na -ion transport in skeleton 20. Zhou W, et al. (2016) Plating a dendrite-free lithium anode with a polymer/ceramic/ structures. Mater Res Bull 11(2):203–220. polymer sandwich electrolyte. J Am Chem Soc 138(30):9385–9388. CHEMISTRY

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