Lithium Cobalt Oxide Coating for High-Temperature Battery Stability
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face issues with decomposed products forming due to reactions between the positive electrode and electrolyte, leading to decreased discharge capacity and voltage, especially when exposed to high temperatures for extended periods.
Innovation Solution
A positive electrode active material composed of a mixture containing lithium cobalt oxide with a rare-earth compound adhered to its surface and lithium nickel cobalt manganese oxide, with the lithium nickel cobalt manganese oxide content between 1% to 50% by mass, is used to suppress decomposition and elution of metals, forming an inactive layer on the electrode surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge voltage of a battery is increased to increase capacity, then the energy density is improved, but the electrolyte decomposes and discharge capacity decreases
Solution Approach 1:
A rare-earth compound coating is applied to the surface of lithium cobalt oxide particles, serving as an intermediary layer between the positive electrode active material and the electrolyte. This coating suppresses direct contact and chemical reactions between the electrolyte and the positive electrode, thereby preventing electrolyte decomposition while allowing the battery to operate at high charge voltages (4.4V or higher) to achieve high energy density without sacrificing discharge capacity
Solution Approach 2:
The invention changes the surface properties of lithium cobalt oxide by coating it with a rare-earth compound, which alters the chemical characteristics of the electrode surface. This parameter change enables the system to withstand higher voltages and temperatures without electrolyte decomposition, resolving the contradiction between high energy density operation and maintained discharge capacity
2Productivity
If the battery is stored at high temperature or subjected to repeated charging-discharging cycles at high temperature, then the battery capacity increases, but decomposed products form and discharge capacity decreases
Solution Approach 1:
The rare-earth compound coating acts as a protective intermediary that prevents harmful chemical reactions between the positive electrode and electrolyte during high-temperature storage and cycling. This intermediary layer remains stable under elevated temperatures, preventing the formation of decomposed products that would otherwise reduce discharge capacity
Solution Approach 2:
The rare-earth compound coating is applied in advance to the surface of lithium cobalt oxide before battery assembly. This preliminary protective action ensures that when the battery undergoes high-temperature storage or repeated cycling, the electrode surface is already protected, preventing electrolyte decomposition and maintaining discharge capacity throughout the battery's operational life
3Use of energy by moving object
If lithium nickel cobalt manganese oxide is added to increase capacity, then the energy density is improved, but metal elution increases and discharge voltage decreases
Solution Approach 1:
The rare-earth compound coating on lithium cobalt oxide serves as a protective barrier that reduces metal elution from the positive electrode active material. By preventing direct contact between the electrolyte and metal surfaces, the coating suppresses metal dissolution into the electrolyte, thereby maintaining stable discharge voltage even when lithium nickel cobalt manganese oxide is used to increase energy density
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
This configuration effectively maintains discharge capacity and voltage even after continuous charging at high temperatures, enhancing the battery's energy density and performance in severe environments.
Implementation Method 1
lithium cobalt oxide having a surface to which a rare-earth compound is partly adhered
Data Source
AI summary
It is an object of the present invention to provide a positive electrode for nonaqueous electrolyte secondary batteries that can suppress decreases in the discharge capacity and discharge voltage even when continuous charging is performed at high temperature and that can also suppress decreases in the discharge voltage and energy density even in the charge and discharge after the continuous charging, and to provide a nonaqueous electrolyte secondary battery that uses the positive electrode. The positive electrode includes a positive electrode active material composed of a mixture containing lithium cobalt oxide 21 having a surface to which an erbium compound 22 is partly adhered and lithium nickel cobalt manganese oxide and a binder. The content of the lithium nickel cobalt manganese oxide is 1% by mass or more and 50% by mass or less relative to the total amount of the positive electrode active material.