Coated LiCoO2 Positive Electrode for High-Voltage Stability
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Solution Overview
Problem
Current lithium secondary batteries with LiCoO2 as the positive electrode active material face limitations in achieving high energy density and long charge-discharge cycle life due to the decay of the crystalline structure at higher charge voltages, leading to reduced thermal stability and increased internal resistance.
Innovation Solution
A nonaqueous secondary battery design incorporating a positive electrode with a lithium-containing transition metal oxide, such as Mg, Ti, Zr, Ge, Nb, Al, or Sn, and a nonaqueous electrolyte containing a compound with at least two nitrile groups to prevent direct contact between the positive electrode and electrolyte, enhancing stability and preventing gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the charge final voltage is increased to higher than 4.2 V to increase charge capacity, then the electric capacity is improved, but the crystalline structure of LiCoO2 decays and charge-discharge cycle life is shortened
Solution Approach 1:
A coating layer comprising at least one metal element selected from Mg, Ti, Zr, Ge, Nb, Al, and Sn is formed on the surface of the LiCoO2 particles. This coating layer acts as an intermediary between the electrolyte and the LiCoO2, preventing direct contact and harmful reactions while allowing lithium ion diffusion, thereby enabling high-voltage charging without structural decay.
Solution Approach 2:
The invention changes the surface composition parameter of the LiCoO2 by adding a coating layer with specific metal elements. This parameter change modifies the surface properties to enhance stability at high voltages while maintaining ion transport, resolving the contradiction between capacity and cycle life.
2Quantity of substance
If the charge final voltage is increased to higher than 4.2 V to increase charge capacity, then the electric capacity is improved, but the thermal stability of the battery deteriorates
Solution Approach 1:
The metal element coating layer serves as a thermal barrier and protective intermediary that prevents direct interaction between the electrolyte and LiCoO2 at high temperatures, thereby maintaining thermal stability even when operating at high charge voltages that would otherwise cause structural decay and safety issues.
3Quantity of substance
If the density of the positive electrode mixture layer is increased to improve battery capacity, then the electric capacity is improved, but the reliability of the battery including storage characteristics gradually decreases
Solution Approach 1:
The invention changes the surface composition parameter of the LiCoO2 by adding a coating layer with specific metal elements. This parameter change modifies the surface properties to enhance stability at high voltages while maintaining ion transport, resolving the contradiction between capacity and cycle life.
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 battery achieves high capacity, stable charge-discharge cycle characteristics, and improved storage characteristics by maintaining the crystalline structure of the positive electrode active material, even at high voltages, thus ensuring safety and efficiency.
Implementation Method 1
a nonaqueous electrolyte containing a compound having at least two nitrile groups in the molecule... preventing direct contact between the positive electrode and electrolyte
Implementation Method 2
the crystalline structure of LiCoO2 decays so that the charge-discharge cycle life may be shortened... maintaining the crystalline structure of the positive electrode active material, even at high voltages
Data Source
AI summary
A nonaqueous secondary battery having a positive electrode having a positive electrode mixture layer, a negative electrode, and a nonaqueous electrolyte, in which the positive electrode contains, as an active material, a lithium-containing transition metal oxide containing a metal element selected from the group consisting of Mg, Ti, Zr, Ge, Nb, Al and Sn, the positive electrode mixture layer has a density of 3.5 g/cm3 or larger, and the nonaqueous electrolyte contains a compound having two or more nitrile groups in the molecule.