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  • Donald J. Pagel

New Cathode Active Materials for Lithium Ion Batteries

Reduced Use of Cobalt in Cathode Active Materials

Cobalt is a widely used element in cathode active materials for lithium ion batteries. For example, lithium cobalt oxide (LiCoO2) and lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC), are widely used cathode active materials. However, a general trend in the LIB industry is to reduce the amount of cobalt used in LIBs. The reasons for this are mainly the high price of cobalt (because of its relative scarcity), and human rights abuses associated with the mining of cobalt. Of course, researchers are also interested in improving the physical characteristics of lithium ion batteries, such as energy density, safety, and durability. These factors have contributed to an upsurge in research into cathode active materials that can reduce or replace cobalt in lithium ion batteries while also improving battery performance. Here are some examples of improved cathode materials taken from newly published patent applications.

Nickel-Rich Cathode Materials

Published U.S. application 2019/0190019 A1 (published June 20, 2019 and assigned to Samsung SDM Co., Ltd.), discloses a cathode active material comprised of LixNiyM1-yO2, where M can be one or more of the metals cobalt, manganese and aluminum, and the percentage of Ni ranges from 50 to 100 mol%. The high nickel content not only lowers the amount of cobalt used in the cathode active material; it also increases the discharge capacity. On the downside, the high nickel content causes swelling problems in the cathode material, probably because of a high content of unreacted lithium in the cathode material. To reduce this swelling problem, the LixNiyM1-yO2 is coated with a film comprised of a rare earth metal hydroxide compound, such as hydroxides of yttrium, cerium, lanthanum, etc. The rare earth hydroxide film allows the high nickel content cathode material to be washed with an aqueous solution during manufacturing which lowers the amount of unreacted lithium, thereby reducing the swelling problem.

Silicon Modified Lithium-Rich Layered Oxides

Another approach to the cobalt and low performance issues in lithium ion batteries is to use a material like, lithium-rich layered oxides (also called HE-NMC) having the formula Li[Lix/3Mn2x/3M1-x]O2, where M = Ni, Mn, Co. Lithium-rich layered oxides have high operating voltage (4.8V) and high specific capacity (> 250mAh/g) but suffer from performance degradation.

Published U.S. application 2019/0252671 A1 (published August 15, 2019 and assigned to GM Global Technology Operations LLC), discloses a way to overcome these degradation issues by using silicon to modify HE-NMC cathode material. The new active cathode material has the formula Li[LiyMna-xSixMbIIIMcII]O2, where MIII is a trivalent metal, preferably cobalt, and MII is a divalent metal, preferably nickel. A preferred composition of the new cathode material is Li[Li0.2Mn0.49Si0.05Ni0.13Co0.13]O2, and methods for preparing these materials are described.

Lithium Sulfur Batteries

Yet another approach to dealing with the cobalt issues in lithium ion batteries is to use a different chemistry entirely. Lithium sulfur batteries do not use cobalt and also have a higher energy density than conventional lithium ion cells. In some configurations of lithium sulfur batteries, the anode comprises lithium metal, and the cathode comprises sulfur and some form of carbon to increase electrical conductivity. During discharge, lithium ions move from the anode to the cathode where various lithium polysulfide salts, such as Li2S2 up to Li2S8, are formed. A primary problem with lithium sulfur batteries is the so-called polysulfide “shuttle” effect where polysulfides formed in the cathode dissolve in the electrolyte and migrate to the anode.

Published U.S. application 2019/0173125 A1 (published June 6, 2019 and assigned to Lyten, Inc.), discloses a configuration for a lithium sulfur battery where the cathode is supported on a first substrate and comprises an active material comprised of particulate carbon and a polysulfide mixture having the formula LixSy, where x = 0 to 2, and y = 1 to 8. The anode is supported on a second substrate and comprises particulate carbon and particulate silicon. The particulate carbon in the cathode and anode comprises carbon nanoparticles comprised of graphene having up to fifteen layers of carbon. It is proposed that the porous structure of the particulate carbon provides pockets that trap the polysulfides formed during charging and discharging, thereby improving battery performance by reducing the migration of polysulfides to the anode.

Batteries for electric vehicles.

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