Positive Electrode Coating Suppresses Voltage Drop
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face a decrease in initial discharge voltage when the positive electrode active material and electrode are exposed to air, due to degradation reactions.
Innovation Solution
A positive electrode comprising lithium transition metal oxide with a rare-earth compound and a lithium-boron compound adhering to its surface, which suppresses the LiOH production reaction and moisture adsorption, maintaining charge-discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge voltage is increased to achieve higher capacity, then the energy density improves, but the decomposition reaction of electrolytic solution at the interface increases causing degradation
Solution Approach 1:
A coating layer containing rare-earth element compound and lithium-boron compound is introduced as an intermediary between the positive electrode active material and the electrolytic solution. This coating layer suppresses the decomposition reaction of the electrolytic solution at the interface, allowing higher charge voltages to be applied without excessive degradation, thereby enabling higher energy density while maintaining reliability.
2Ease of manufacture
If the positive electrode active material is exposed to air during handling, then manufacturing ease improves, but moisture adsorption occurs causing decrease in initial discharge voltage
Solution Approach 1:
The coating layer containing rare-earth element compound and lithium-boron compound is applied in advance to the surface of the positive electrode active material before air exposure occurs. This preliminary protective action prevents moisture adsorption from air, allowing the electrode material to be handled more easily without compromising the initial discharge voltage.
3Reliability
If LiOH production reaction is suppressed to maintain discharge voltage, then charge-discharge characteristics are maintained, but coating complexity increases
Solution Approach 1:
A composite coating layer containing both rare-earth element compound and lithium-boron compound is employed. This composite structure effectively suppresses the LiOH production reaction and maintains charge-discharge characteristics. The two compounds work synergistically to provide comprehensive protection while managing coating complexity through a defined dual-component system.
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 combination of rare-earth and lithium-boron compounds effectively prevents the degradation of initial charge-discharge characteristics by reducing moisture adsorption and LiOH production, thereby maintaining the discharge voltage.
Implementation Method 1
a rare-earth compound and a lithium-boron compound adhere to surfaces of the lithium transition metal oxide
Implementation Method 2
suppresses the LiOH production reaction and moisture adsorption
Implementation Method 3
suppresses the LiOH production reaction
Data Source
AI summary
There is provided a positive electrode for nonaqueous electrolyte secondary batteries in which a decrease in the initial discharge voltage can be suppressed even when a positive electrode exposed to the air is used. The positive electrode for a nonaqueous electrolyte secondary battery according to an aspect of the present invention contains a lithium transition metal oxide constituted by a secondary particle formed by aggregation of primary particles. A rare-earth compound adheres to at least part of a surface of the secondary particle, and a compound containing lithium and boron adheres to at least part of the surface of the secondary particle and at least part of an interface between primary particles aggregated at the surface of the secondary particle.