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Update(MM/DD/YYYY):11/27/2019

Negative Electrode for High Capacity Lithium-ion Secondary Battery That Does Not Degrade

– Use of thin silicon oxide nano-film realizes negative electrode capacity five times greater than graphite electrode –


Researchers: MAMIYA Mikito, Senior Researcher, and AKIMOTO Junji, Leader, Energy Conversion and Storage Materials Team, Advanced Coating Technology Research Center.

Key Point

For the developed negative electrode, a nanometer-scale layered structure of silicon monoxide (SiO) is formed through vapor deposition. The electrode realizes approximately five times the capacity of a graphite electrode (the current mainstream electrode), corresponding almost exactly with the theoretical capacity of silicon monoxide.

Figure
Comparison of the properties between previous electrodes and developed one


Background

Possessing from several times to more than ten times the theoretical capacity of graphite and offering the advantage of stable supply, silicon-based negative electrodes are considered the strongest candidates to be employed as the negative electrodes in next-generation lithium-ion secondary batteries. Among these, SiO is a promising active material, due to its theoretical capacity of 2007 mAh/g, as compared to 372 mAh/g for graphite. SiO is easily vaporized under conditions of high temperature and reduced pressure. It offers the advantage of allowing nanometer-scale SiO thin films to be formed on substrates via vapor deposition. However, due to its low electrical conductivity, there has previously been no concept of directly using a thin film formed by vapor deposition as an electrode.

New results

For the developed negative electrode for lithium-ion secondary batteries, a nanometer-scale thin SiO film was formed on a conductive substrate using vapor deposition and a conductive additive was then layered on this thin film. The new electrode achieves 2000 mAh/g, approximately five times 372 mAh/g for a graphite negative electrode, corresponding almost exactly to the theoretical capacity of SiO (2007 mAh/g). In addition, the developed electrode maintained its capacity even after more than 500 charge-discharge cycles, clearly demonstrating that it displays long life at high capacity. This can be expected to increase the energy density of negative electrodes, and advance the realization of increased capacity and reduced size in lithium-ion secondary batteries.

Future Research Plans

This electrode requires a large capacity in the 1st charging process. If it is used as is, the lithium of the positive electrode will be consumed and the performance will immediately drop. To avoid this problem, the electrode must be pre-doped with lithium before a battery is fabricated by combining a positive electrode and this one. The performance verification is underway with the objective of practical application.







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