Lithium ion battery

Abstract

The invention provides a lithium ion battery. The lithium ion battery comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane; a positive active material in the positive pole piece comprises LixCoyM<1-y>O<2-z>Qz, x is greater than or equal to 0.5 and less than or equal to 1.2, y is greater than or equal to 0.8 and less than 1.0, z is greater than or equal to 0 and less than or equal to 0.1, M is selected from one or more of Al, Ti, Zr, Y and Mg, and Q is selected from one or more of F, Cl and S. The electrolyte contains an additive A and an additive B, wherein the additive A is a polynitrile six-membered nitrogen heterocyclic compound with low oxidation potential, and the additive Bis an aliphatic dinitrile or polynitrile compound with high oxidation potential. The lithium ion battery disclosed by the invention has excellent cycle performance and storage performance, and particularly has excellent cycle performance and storage performance under the conditions of high temperature and high voltage.

Description

technical field [0001] The present application relates to the field of energy storage materials, in particular, to a lithium ion battery. Background technique [0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages of high energy density, high output power, long cycle life and low environmental pollution. The current demand for lithium-ion batteries is: high voltage, high power, long cycle life, long storage life and excellent safety performance. [0003] LiCoO is currently widely used in lithium-ion batteries 2 As a cathode active material, LiCoO in the fully discharged state 2 and half-charged Li 0.5 CoO 2 (4.2V vs. Li) cycle performance is relatively stable, so the actual lithium ions that are actually used are only 1 / 2 of their actual lithium ion content. And when the voltage is greater than 4.2V, LiCoO 2 The remaining 1 / 2 content of lithium ions can continue to be extracted, but in the process of...

AI Technical Summary

Problems solved by technology

And when the voltage is greater than 4.2V, LiCoO 2 Lithium ions in the remaining 1 / 2 content can continue to be removed, but during the deep delithiation process, Co 3+ Will be oxidized to very unstable Co 4+ , together with the surface oxygen that has lost a large number of electrons, oxidizes the electrolyte. At this time, a large amount of gas will be generated inside the battery and cause the battery to bulge.

At the same time, due to the corrosion effect of HF in the electrolyte on the surface of the positive electrode, the Co 4+ After being dissolved in the electrolyte, it deposits on the surface of the negative electrode, catalyzes the reduction of the electrolyte, and also produces a large amount of gas that causes the battery to bulge

In addition, due to the large overlap between the 3d energy level of Co and the 2p energy level of O, deep delithiation will also cause the lattice oxygen to lose a large amount of electrons, making LiCoO 2 The unit cell shrinks violently along the c-axis, which induces instability or even collapse of the local bulk phase structure, and finally causes LiCoO 2 Loss of active sites, rapid loss of lithium-ion battery capacity

Therefore LiCoO 2 Very poor performance when used in high voltage regimes greater than 4.2V

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