8 s US005705291A United States Patent 19 11 Patent Number: 5,705,291 Amatucci et al. 45 Date of Patent: Jan. 6, 1998

54 RECHARGEABLE BATTERY CELL HAVING 4,465,747 8/1984 Evans ...... 429,194 SURFACE-TREATED LTHATED 4,977.024 12/1990 Morita et al...... 427/215X INTERCALATON POSITIVE ELECTRODE 5,277,995 1/1994 Ruka et al...... 29/623.5 X 5,292,601 3/1994 Sugeno et al...... 429/232X 75 Inventors: Glenn G. Amatucci, Raritan; Jean-Marie Tarascon, Martinsville, FOREIGN PATENT DOCUMENTS both of N.J. 7-192720 7/1995 Japan ...... HOM 4/O2 73 Assignee: Bell Communications Research, Inc. Primary Examiner-Stephen Kalafut Morristown, N.J. Attorney, Agent, or Firm-Lionel N. White; Joseph Giordano 21 Appl. No.: 630,807 57 ABSTRACT 22 Fed: Apr. 10, 1996 A rechargeable lithiated intercalation battery cell having 51 Int. Cl. ... O1M 4/62 reduced self-discharge comprises a negative electrode, a 52) U.S. Cl...... 429/137; 429/232; 29/623.5 nonaqueous electrolyte, and a positive electrode wherein the 58) Field of Search ...... 427/215; 29/623.5; surfaces of the aggregate lithiated intercalation composition 429/137,232 particulates comprising the positive cell electrode have been coated with a passivating layer of a composition comprising 56 References Cited a borate, lithiated borate, aluminate, lithiated aluminate, silicate, lithiated silicate, or mixtures thereof. U.S. PATENT DOCUMENTS 3,522,078 7/1970 May et al...... 427/25 11 Claims, 5 Drawing Sheets

3. O

2. O

O

None HBO3 B2O3 LiMn2O4 Treatment U.S. Patent Jan. 6, 1998 Sheet 1 of 5 5,705,291

30

2 O | 1 O o6 23 LiMn2O4. Surface Area - m FIG. 1

1 OO 90 8O 70 60 50 O 50 100 150 Cycle Number FIG. 2 U.S. Patent Jan. 6, 1998 Sheet 2 of 5 5,705,291

3. O

2. O

O

O None HBO B2O3 LiMn2O4 Treatment FIG. 3 U.S. Patent Jan. 6, 1998 Sheet 3 of 5 5,705,291

4.5

4.O

i 3.5 0.5% HBO 3.O 0.2 0.4 0.6 0.8 1.0 X in LiMn2O4 FIG. 4

i 1.0% HBO 3.0 0.2 0.4 0.6 0.8 1.O X in LiMn2O4 FIG. 5 U.S. Patent Jan. 6, 1998 Sheet 4 of 5 5,705,291 4.5

D 4.O CD O) S 3.5 2.0% HBO 3.0 0.2 0.4 0.6 0.8 1.0 X in LiMn2O4 FIG. 6

4.5

D 4.O CD O) S 3.5 4.0% HBO 3.O 0.2 0.4 0.6 0.8 1.O X in LiMn2O4. FIG. 7 U.S. Patent Jan. 6, 1998 Sheet S of 5 5,705,291

S OCN y O yO LO O % - SSO Aloedeo eqSueneu 5,705,291 1. 2 RECHARGEABLE BATTERY CELL HAWNG self-discharge. Another object of the present invention is to SURFACE-TREATED L THATED provide a novel lithium intercalation cell having an NTERCALATON POSITIVE ELECTRODE improved reduction in self-discharge upon storage at tem BACKGROUND OF THE INVENTION peratures up to about 55° C. These objects, among others, have been achieved in the This invention relates to a rechargeable lithiated interca present invention by means of a novel lithium intercalation lation battery cell comprising a negative electrode, a non cell in which the surfaces of aggregate lithiated intercalation aqueous electrolyte, and a positive electrode, and, composition particulates comprising the positive cell elec particularly, to such a cell which exhibits a greatly reduced trode have been passivated by coating or encapsulation in a level of self-discharge by virtue of a surface-passivating layer of a composition comprising aborate, lithiated borate, treatment of the lithiated intercalation composition particu aluminate, lithiated aluminate, silicate, or lithiated silicate. lates comprising the positive electrode. Such a coating not only reduces the surface area. and thus Recent advances in rechargeable electrolytic battery cell the degree of activity, of the potentially catalytic particulate technology have provided cells in which lithium metal is aggregates, but also provides a barrier layer which, while replaced with a material capable of reversibly intercalating 15 limiting contact between the electrolyte and the positive lithium ions, thereby providing a so-called "rocking chair" electrode particulates, does not seriously deter the passage of cell, or lithium-ion intercalation cell, in which lithium ions Litions. "rock” between the intercalation electrodes during the In a preferred embodiment of the present invention, the charging/recharging cycles. Such a lithium metal-free "rock surfaces of these particulates are coated with a layer of a ing chair” cell may thus be viewed as comprising two 20 lithium-ion-absorbing electrode "sponges” separated by a composition comprising boron oxide, boric acid, lithium lithium-ion conducting electrolyte usually comprising a Li hydroxide, aluminum oxide, lithium aluminate, lithium salt dissolved in a non-aqueous solvent or mixture of such metaborate, silicon dioxide, lithium silicate, or mixtures solvents. This type of cell has been described by various thereof. In another embodiment of the present invention, the investigators, including Murphy et al. J. Electrochem. Soc., coating of the surfaces of these particulates with a selected 126, 349 (1979); Lazzari et al., J. Electrochem. Soc., 127 composition is effected by annealing at a temperature in 773 (1980); Armand, in "Materials for Advanced Batteries." excess of about 400° C., preferably in the range of about Murphy et al., eds., Plenum Press, New York, p. 145 (1980); 500° C. to 800° C., to fuse the composition and allow it to and Guyomard et al., U.S. Pat No. 5,192,629. flow and evenly coat the particulates. The output voltage of a Li-ion cell is determined by the BRIEF DESCRIPTION OF THE DRAWTNG difference between the electrochemical potential of Li within the two lithium sponges. Thus, to obtain a large The present invention will be described with reference to output voltage and large energy values, one needs to employ the accompanying drawing of which: as positive and negative electrodes lithium sponges that can FIG. 1 is a chart depicting total and inreversible portions intercalate lithium at high and low potential, respectively. 35 of the self-discharge of battery cells during storage at 55° C. Among the materials which can replace lithium metal as the as a function of the surface area density of LiMnO, negative electrode, carbon provides an advantageous com electrode material; promise between a large specific capacity and reversible FIG. 2 is a graph depicting loss of initial capacity as a cycling behavior. Positive electrode materials suitable in function of the number of charge/discharge cycles for cells such lithium-ion cells are the layered LiCoO, and LiNiO, having differing LiMn2O electrode surface area density; intercalation compounds, and the three-dimensional spinel FIG. 3 is a chart depicting the catalytic activity of phase LiMn2O. LiMnO, electrode composition, before and after treatment A common feature of rechargeable Li-ion cells based on according to the present invention, as measured by catalytic these oxides as positive electrodes is that they deintercalate conversion of CO to CO; lithium ions at an average potential of 4W, and, therefore, 45 must be charged up to voltages greater than 4 W so as to FIGS. 4-7 are graphs of the electrolytic performance of utilize their full capacity. An inherent problem with this battery cells as represented by intercalated lithium as a lithium ion technology is related to the use of highly function of charge/discharge voltage in LiMnO positive oxidizing positive electrodes and their high charging electrodes having differing degrees of treatment according to voltages, namely, the risk of self-discharge. This self 50 the present invention; and discharge phenomenon, attributed in part to catalyzed elec FIG. 8 is a chart of the comparative irreversible capacity trolyte decomposition by Guyomard et al., Journal of Power loss of battery cells comprising LiMnO, positive electrodes Sources, 54, 92 (1995), can, even at low levels, jeopardize having differing degrees of treatment according to the cycle life and capacity, as well as the safety of the cells. present invention. Attempts to control the deleterious electrolyte 55 decomposition, such as by elevating decomposition reaction DESCRIPTION OF THE INVENTION threshold temperatures, as suggested in Japanese Applica Rechargeable Li-ion battery cells of the present invention tion No.7-192720, or by neutralizing acidic impurities, as in are preferably of the type generally described in U.S. Pat. U.S. Pat. No. 4,465.747, have not, however, proven signifi No. 5,460.904, the disclosure of which is incorporated cantly successful. Therefore, there remained a need in the herein by reference. Such a battery cell comprises a unitary industry for a rechargeable, lithium intercalation battery cell laminate of a positive electrode composition layer with an which is resistant to self-discharge, even at elevated tem associated current collector member, an intermediate sepa peratures up to about 55° C. rator layer having incorporated therein a non-aqueous electrolyte, and a negative electrode composition layer with SUMMARY OF THE INVENTION 65 an associated current collector member. When initially An object of the present invention is to provide a novel assembled for lamination, the battery structure components lithium intercalation cell having an improved reduction in typically include: as the positive electrode layer, a 300 m 5,705,291 3 4 thick film of 6 parts of carbon black and 56 parts by weight Adjustment of the surface morphology of the intercalation of a Li-ion intercalation compound, such as a LiMnO, compound has therefore been addressed as a means of wherein 0lithium hydroxide, aluminum oxide, promoted by the catalytic action of the intercalation com lithium aluminate, lithium metaborate, silicon dioxide, pound electrode component, e.g., LiMn2O. This deleterious lithium silicate, or mixtures thereof. activity within a rechargeable battery cell is believed to proceed as: EXAMPLE 1. (1) Electrolyte-Electrolyte'+e (Irreversible) In order to test the utility of this approach, a LiMnO, (2)MnO-e-Hi-Li,Mn2O (Reversible) in which the powder was prepared by annealing LiCO and MnO, latter reaction results in an immediate, yet recoverable, precursors according to the procedure described in U.S. Pat. loss in available cell output, or capacity, while the No. 5.425,932. The resulting intercalation compound was former reaction, resulting in electrolyte decomposition, 35 used in this and the other examples of this specification. A leads to permanent loss in cell capacity. measure of the LiMnO, powder was intimately mixed by The hypothesized catalysis of the irreversible electrolyte grinding with about 1% by weight of HBO and the mixture decomposition reaction by the positive electrode intercala was then briefly heated at about 800° C. to fuse the HBO, tion compound, such as LiMnO, gains support from the into an amorphous borate film which coated the surfaces of fact that, as is typical of surface-dependent catalytic the LiMnO, particulates. The resulting material was readily reactions, the ineversible loss of cell capacity varies as a comminuted to yield a fine powder which appeared, under function of the surface area density of the aggregate par SEM examination, to have lost its sharp particulate profile in ticulates of that compound. This activity may be seen in favor of the smoother aggregate surface features of the FIGS. 1 and 2 which depict the greater total and irreversible borate barrier overcoating. capacity losses during charged storage at about 55 C., as The efficacy of the borate coating in curtailing the normal well as the greater overall capacity loss over multiple 45 catalytic action of LiMnO, was then tested by exposing the charge/discharge cycles, exhibited by a cell having greater coated LiMnO, powder at about 450° C. to a 20 cm/min LiMnO, electrode material surface area, i.e., smaller mate flow of N containing 4% O and 5% CO on the premise that rial particle size. the extent of oxidation of the CO to CO in the reaction: It is apparent, therefore, that a significant factor in less ening the extent of self-discharge and irreversible loss of 50 capacity in rechargeable Li-ion battery cells is the limitation would provide an indication of the extent of catalysis by of the active surface area of the highly oxidizing positive LiMn2O4. A similar test utilizing untreated LiMn2O4 pow electrode material, such as LiMnO. Since such surface der provided a datum for the comparative evaluation. The area is influenced by both particulate size and the surface results of these tests indicated that, indeed, the borate barrier morphology, it is an objective of the present invention to 55 effect control of these two parameters of the material. coat treatment according to the invention decreased the An initial approach to reducing the surface area density of generation of CO, and thus the catalytic activity of the LiMnO, for example, has been in the synthesis of the LiMnO, by about 95%. A repeat of the treatment proce compound through the use of LiCO and LiOH reactants, dure utilizing BO produced substantially similar results, in preference to LiNO, since there are thus obtained all of which are depicted in FIG. 3 with reference to moles LiMnO, powders of larger particle size having a surface of CO, generated in the test. area, as determined by common BET analysis, in the range Limitation of the catalytic action of a treated electrode of 0.2 mig to 0.8 mig, as compared with the 3.6 m/g compound on the oxidation of electrolyte did not alone surface area powders obtained with LiNO. Although some establish that such a material could be effectively employed what successful, this expedient, even when supplemented in a Li-ion battery cell, however. For this purpose, the with screening to remove a significant proportion of finer 65 electrolytic function of the electrode material, particularly in particles, did not sufficiently alleviate battery cell self its support of the flow of Li ions, must continue, uninhib discharge and irreversible capacity loss. ited by the barrier effect of the borate coating. Efficacy of 5,705,291 5 6 treated LiMnO, as a component of positive battery cell intercalation compound particulates, the surfaces of which electrode compositions was therefore tested. particulates are coated with a passivating layer comprising an annealed coating composition comprising boron oxide, EXAMPLE 2 boric acid, lithium hydroxide, aluminum oxide, lithium Portions of LiMnO, powder were treated as in Example 5 aluminate. lithium metaborate, silicon dioxide, lithium 1 with varying amounts of HBO, namely, 0.5%, 1.0%, silicate, or mixtures thereof. 2.0%, and 4.0% by weight, respectively, relative to the 2. The rechargeable lithiated intercalation cell having amount of LiMnO. The treated LiMnO, powders were reduced self-discharge according to claim 1, wherein said then used, in typical formulations earlier-noted with respect coated passivating layer is prepared by annealing said coat to U.S. Pat. No. 5.460.904, to prepare rechargeable Li-ion O ing composition at a temperature in excess of 400° C. intercalation battery test cells. These cells were then sub 3. The rechargeable lithiated intercalation cell having jected to charge/discharge cycling over the range of 3 W to reduced self-discharge according to claim 1, wherein said 4.5 V at a constant 10 mA as described in that patent and coating composition is present in an amount of about 0.4% their electrolytic performance over the first cycle was plotted to 0.8% by weight relative to the amount of the lithiated as shown in FIGS. 4–7. The exhibited degree of irreversible 5 intercalation compound. capacity loss during this cycle indicated, on the basis of past 4. The rechargeable lithiated intercalation cell having performance experience, that practical battery cells would be reduced self-discharge according to claim 3, wherein said limited to the use of electrode material treated with less than coating composition is present in an amount of about 0.6% about 2% borate compound, with the range of about 0.6% to by weight relative to the amount of the lithiated intercalation 1% being generally preferred. compound. 5. The rechargeable lithiated intercalation cell having To further ensure acceptable Lition conductivity through reduced self-discharge according to claim 1, wherein said the barrier coating of treated intercalation compound elec lithiated intercalation electrode comprises LiMnO, where trode material, lithiated treatment compounds were exam 0