Nonaqueous Battery DCR Reduction via Rare Earth Coating
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries experience an increase in direct current resistance (DCR) after charge discharge cycles, deteriorating their output characteristics despite previous techniques aimed at improving capacity and discharge performance.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a positive electrode with lithium transition metal oxide particles, where secondary particles of a rare earth compound are attached to recesses between primary particles, and magnesium is dissolved within the lithium transition metal oxide, reducing interface alterations and breakages during charge discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Group III element is added to restrain reaction between positive electrode active material and electrolytic solution, then charge storage characteristics are improved, but output characteristics deteriorate due to increased DCR
Solution Approach 1:
The patent applies local quality by attaching rare earth compound particles specifically to recess portions between primary particles on the surface of secondary particles, rather than uniform distribution. This localized attachment protects critical interface regions where reactions occur most intensely, improving charge storage characteristics while minimizing impact on overall conductivity and output characteristics.
Solution Approach 2:
The patent creates a composite structure by combining lithium transition metal oxide secondary particles with rare earth compound particles. This composite material approach allows the base particles to maintain good conductivity for output characteristics while the attached rare earth compounds provide protection against degradation for charge storage characteristics, resolving the contradiction between the two performance aspects.
2Quantity of substance
If charge voltage is increased to improve capacity, then energy density is improved, but reaction between positive electrode active material and electrolytic solution increases causing deterioration in charge storage characteristics
Solution Approach 1:
The patent applies preliminary action by pre-attaching rare earth compound particles to the surface of positive electrode active material particles before battery assembly. This preliminary protective layer is already in place when the battery begins operation, preventing direct contact and reaction between the active material and electrolytic solution from the outset, thereby maintaining charge storage characteristics even at increased charge voltages.
Solution Approach 2:
The rare earth compound particles serve as an intermediary layer between the positive electrode active material and the electrolytic solution. This intermediate layer prevents direct harmful reactions while allowing ionic transport, enabling the battery to operate at higher charge voltages without degradation of charge storage characteristics.
3Productivity
If magnesium is dissolved in positive electrode active material to improve discharge performance, then discharge characteristics are improved, but DCR increases after charge discharge cycles
Solution Approach 1:
The patent applies local quality by concentrating rare earth compound particles at the surface regions and interfaces of primary particles, where degradation and DCR increase occur most prominently during cycling. This localized protection preserves the bulk magnesium-doped structure that provides good discharge performance while protecting the critical surface regions from degradation that would increase DCR.
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 results in a smaller increase in DCR after charge discharge cycles, enhancing the battery's output characteristics by preventing surface and internal alterations of the positive electrode active material.
Implementation Method 1
dissolving magnesium (Mg) into a positive electrode active material decreases the crystallinity of the positive electrode
Implementation Method 2
a secondary particle of a rare earth compound is attached to a recess formed between adjacent primary particles of the lithium transition metal oxide
Data Source
AI summary
An object of the present invention is to provide a nonaqueous electrolyte secondary battery that can attain a smaller increase in direct current resistance after charge discharge cycles. An aspect of the invention resides in a nonaqueous electrolyte secondary battery wherein a positive electrode active material includes a secondary particle formed by aggregation of primary particles of a lithium transition metal oxide, and a secondary particle formed by aggregation of primary particles of a rare earth compound. On a surface of the secondary particle of the lithium transition metal oxide, the secondary particle of the rare earth compound is attached to a recess formed between adjacent primary particles of the lithium transition metal oxide in such a manner that the secondary particle of the rare earth compound is attached to each of the primary particles forming the recess. The lithium transition metal oxide includes magnesium dissolved therein.