LiCoO2 Cathode and Electrolyte Additives for High-Voltage Cycling
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Solution Overview
Problem
Lithium-ion batteries using LiCoO2 as the positive active material suffer from poor performance under high-voltage conditions due to lattice deformation, instability of the bulk structure, and rapid capacity degradation.
Innovation Solution
A lithium-ion battery design incorporating a metal ion M-doped lithium cobalt oxide material Lix1Coy1M1-y1O2-z1Qz1 as the positive active material, combined with a polynitrile six-membered nitrogen-heterocyclic compound and an aliphatic dinitrile or polynitrile compound as additives in the electrolyte to enhance structural stability and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO2 is used as positive active material and voltage is increased above 4.2V to extract more lithium ions, then capacity is improved, but structural stability deteriorates due to Co4+ oxidation and lattice oxygen electron loss
Solution Approach 1:
A coating layer comprising at least one of a metal oxide, metal hydroxide, metal carbonate, metal phosphate, or metal sulfide is applied to the surface of the LiCoO2 positive active material particles. This coating layer acts as an intermediary barrier that protects the bulk LiCoO2 structure from direct exposure to the electrolyte, preventing HF corrosion and stabilizing surface Co4+ species, thereby enabling high-voltage operation above 4.2V without structural collapse
Solution Approach 2:
The patent modifies the surface properties of LiCoO2 by changing its chemical composition through coating with metal oxides, hydroxides, carbonates, phosphates, or sulfides. This parameter change at the surface level allows the material to operate stably at higher voltages by suppressing parasitic reactions while maintaining bulk structural integrity
2Quantity of substance
If deep delithiation is performed to increase capacity, then more lithium ions are extracted, but gas production increases due to electrolyte oxidation and HF corrosion
Solution Approach 1:
The coating layer serves as a protective intermediary that prevents direct contact between the LiCoO2 surface and the electrolyte. This barrier suppresses the oxidation of electrolyte by surface Co4+ and prevents HF corrosion, thereby eliminating the primary sources of gas generation during deep delithiation at high voltages
Solution Approach 2:
The coating layer transforms the potentially harmful high-voltage operation into a beneficial process by using the coating material itself as a sacrificial protective layer that stabilizes surface Co4+ species and prevents them from attacking the electrolyte, thereby converting what would be a harmful oxidation process into a stable operational state
3Quantity of substance
If high voltage operation is implemented to increase energy density, then more lithium ions are utilized, but cycle life decreases due to structural degradation
Solution Approach 1:
The coating layer acts as a protective intermediary that isolates the LiCoO2 bulk structure from the harsh electrolyte environment during high-voltage cycling. This barrier prevents progressive structural degradation, maintaining lithium ion utilization and extending cycle life
Solution Approach 2:
The coating layer is applied in advance before battery operation to pre-protect the LiCoO2 surface. This preliminary protective action prevents structural degradation from occurring during subsequent high-voltage cycling, thereby extending cycle life before any damage can accumulate
Data Source
AI summary
The present application provides a lithium-ion battery and an apparatus, the lithium-ion battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separation film. The positive active material in the positive electrode sheet includes Lix1Coy1M1-y1O2-z1Qz1, 0.5≤x1≤1.2, 0.8≤y1<1.0, 0≤z1≤0.1, and M is selected from one 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, the additive A is a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential, and the additive B is an aliphatic dinitrile or polynitrile compound with a relatively high oxidation potential. The lithium-ion battery of the present application has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.