Positive Active Material Particle Segmentation for Resistance Stability
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Solution Overview
Problem
Secondary batteries, such as lithium ion batteries, experience increased resistance due to repeated charge-discharge cycles, which affects their performance and longevity.
Innovation Solution
The energy storage device incorporates an electrode assembly with a positive electrode containing primary particles that do not form secondary particles or secondary particles formed by aggregation of primary particles, with a specific diameter ratio and BET specific surface area, and is housed in a case under pressure to suppress expansion and crack generation during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the positive active material contains secondary particles formed by aggregation of primary particles, then the battery can be manufactured with conventional processes, but the resistance increases due to crack formation during charge-discharge cycles
Solution Approach 1:
The positive active material is divided into primary particles that remain separate and do not aggregate into secondary particles. This segmentation prevents crack formation at particle boundaries during charge-discharge cycles, maintaining structural integrity and reducing resistance increase over time.
Solution Approach 2:
The invention changes the particle size distribution parameter by controlling the formation process to prevent secondary particle aggregation. By maintaining primary particles as discrete entities rather than allowing them to form aggregated secondary particles, the structural stability during cycling is improved.
2Reliability
If the electrode assembly is not pressed, then the manufacturing process is simpler, but the resistance increases due to expansion and crack generation during charging and discharging
Solution Approach 1:
The electrode assembly is pressed during manufacturing before assembly into the battery. This preliminary pressing action pre-compresses the positive active material particles, preventing expansion and crack formation during subsequent charge-discharge cycles, thereby maintaining low resistance stability.
Solution Approach 2:
The pressing operation changes the density and compaction parameter of the positive active material layer. By applying pressure during manufacturing, the particle arrangement is optimized to prevent expansion during cycling, resolving the contradiction between simple manufacturing and resistance stability.
3Productivity
If the positive active material has large surface contact area with electrolyte, then the charge-discharge rate is faster, but the resistance increases due to more crack formation
Solution Approach 1:
The positive active material consists of discrete primary particles rather than aggregated secondary particles. This segmentation provides sufficient surface area for fast charge-discharge while preventing crack formation at particle boundaries, as each primary particle remains structurally intact during cycling.
Data Source
AI summary
An energy storage device according to one aspect of the present invention includes: an electrode assembly including a positive electrode, a negative electrode, and a separator; a nonaqueous electrolyte; and a case for housing the electrode assembly and the nonaqueous electrolyte, in which the positive electrode contains a positive active material, the positive active material contains a plurality of particles satisfying at least one of conditions (1) and (2) below, and the electrode assembly is in a pressed state. (1) A plurality of primary particles that do not form secondary particles (2) A plurality of secondary particles formed by aggregation of a plurality of primary particles, having a ratio of an average diameter of the secondary particles to an average diameter of the primary particles that form the secondary particles of less than 11