LiCoO2 Lithium-Ion Battery Electrolyte for High-Voltage Cycle Stability
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Solution Overview
Problem
Lithium-ion batteries using LiCoO2 as a positive active material face instability and capacity loss when operated at high voltages greater than 4.2 V due to deep delithiation, leading to lattice deformation, gas production, and corrosion, which affects their cycle and storage performance.
Innovation Solution
A lithium-ion battery design incorporating a metal ion-doped lithium cobalt oxide material (Li x1 Co y1 M 1-y1 O 2-z1 Q z1) with a polynitrile six-membered nitrogen-heterocyclic compound (additive A) and an aliphatic dinitrile or polynitrile compound (additive B) in the electrolyte, where additive A forms a stable complex layer to passivate the positive active material and additive B repairs the layer during cycling, reducing structural degradation and gas production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If LiCoO2 is used as positive active material and voltage is increased above 4.2 V to extract more lithium ions, then battery capacity is improved, but lattice deformation and structural instability occur
Solution Approach 1:
A coating layer comprising at least one of a metal oxide layer and a metal phosphate layer is formed on the LiCoO2 positive active material. This coating layer acts as an intermediary between the LiCoO2 and the electrolyte, preventing direct contact and harmful reactions while allowing lithium ion transport, thereby enabling stable operation at high voltages above 4.2V without lattice deformation
Solution Approach 2:
The patent modifies the surface properties of LiCoO2 by changing its chemical composition through coating with metal oxides or metal phosphates. This parameter change in surface chemistry allows the material to operate stably at higher potentials without suffering from the lattice instability that plagues uncoated LiCoO2
2Quantity of substance
If deep delithiation is performed to utilize remaining lithium ions, then battery capacity is improved, but gas production and corrosion increase
Solution Approach 1:
The coating layer of metal oxide or metal phosphate serves as a protective intermediary that prevents direct contact between the LiCoO2 surface and the electrolyte. This eliminates the source of gas-generating side reactions and corrosion, allowing deep delithiation to proceed without producing harmful gases
Solution Approach 2:
The patent transforms the potentially harmful high-voltage operation and deep delithiation processes into beneficial outcomes by using the coating layer to suppress harmful side reactions. The conditions that would normally cause gas production and corrosion are converted into opportunities for achieving higher capacity while maintaining stability
3Power
If high voltage operation is maintained to improve energy density, then battery performance is improved, but impedance increases and cycle life decreases
Solution Approach 1:
The metal oxide or metal phosphate coating layer acts as a stable intermediary interface that remains intact during high-voltage operation and cycling. It prevents impedance buildup by blocking direct interaction between LiCoO2 and electrolyte decomposition products, thereby maintaining low impedance and long cycle life even at high voltages
Solution Approach 2:
The coating layer is formed on the LiCoO2 surface before the battery is put into service. This preliminary protective action prevents subsequent degradation, impedance increase, and capacity loss that would normally occur during high-voltage cycling, thereby extending cycle life from the outset
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly improves the cycle and storage performance of lithium-ion batteries under high-temperature and high-voltage conditions by reducing lattice deformation, gas production, and impedance, leading to enhanced capacity retention and reduced thickness expansion.
Implementation Method 1
additive A forms a stable complex layer to passivate the positive active material
Implementation Method 2
additive B repairs the layer during cycling
Implementation Method 3
lithium-ion battery includes an electrode assembly and an electrolyte
Data Source
Figure 1~2
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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, 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 relative ly 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.