Lithium Cobaltate Cathode Structure for High-Voltage Cycle Stability
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Solution Overview
Problem
The challenge is to enhance the compaction density and cycle performance of lithium cobaltate-based positive electrode pieces in batteries, which are limited by their irregular structure and irreversible phase transitions at high charging voltages, leading to capacity attenuation and structural destruction.
Innovation Solution
A positive electrode piece with a regular morphological structure is developed, featuring a positive electrode active material with a specific crystal phase structure and accordion stacking, achieved through cross-section polishing and SEM imaging, along with a preparation method involving ion exchange reactions and high-temperature sintering, resulting in improved conductivity and compaction density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If lithium cobaltate with irregular sphere structure is used as positive electrode active material, then the battery can operate, but the compaction density of the positive electrode piece is limited and cannot be improved
Solution Approach 1:
The patent applies asymmetry by transitioning from spherical particles to rectangular plate-like particles with specific aspect ratios. The rectangular shape with length-to-thickness ratio ≥3 creates asymmetric geometry that enables better stacking and higher compaction density in the electrode structure
Solution Approach 2:
The patent changes the morphological parameters of the active material particles by controlling the crystal growth process to form rectangular plates with specific dimensions (length-to-thickness ratio ≥3). This parameter change from spherical to rectangular geometry directly improves compaction density
2Use of energy by moving object
If charging voltage is increased to ≥4.55V to improve energy density, then the battery capacity increases, but lithium cobaltate undergoes irreversible phase transition from O3 to H1-3 leading to accelerated capacity attenuation and structure destruction
Solution Approach 1:
The patent changes the crystal phase parameter of lithium cobaltate by controlling the formation process to obtain the O3 phase with specific XRD characteristics (peak 002 at 18.6°±0.5°, peak 102 at 41.7°±0.5°, peak 103 at 47.1°±0.5°). This phase parameter change enables stable operation at high voltage ≥4.55V without irreversible transition to H1-3 phase
Solution Approach 2:
The patent applies beforehand cushioning by optimizing the particle morphology (rectangular plates with aspect ratio ≥3) and crystal phase (O3 phase) in advance to prevent the irreversible phase transition that would occur during high-voltage charging. The pre-optimized structure resists the destabilizing effects of high voltage
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 solution significantly increases the discharge gram capacity and structural stability of the battery, leading to better cycle performance and capacity retention, with a capacity retention rate of 80% or more after 500 cycles at high voltage.
Implementation Method 1
mixing the compound containing cobalt element and sodium element with a compound containing lithium into deionized water for ion exchange reaction
Implementation Method 2
drying the mixed material after mixing evenly, and then sintering the dried mixed material to obtain the compound NaxCoO2 containing at least Co and Na
Data Source
AI summary
The present application provides a positive electrode piece, a battery and an electric device. A first aspect of the present disclosure provides a positive electrode piece, the positive electrode piece includes a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material; in a plane composed of a length direction and a thickness direction of the positive electrode piece, particles of the positive electrode active material have a longest distance a in the length direction of the positive electrode piece, and have a longest distance b in the thickness direction of the positive electrode piece, and in a region not less than 25 μm*25 μm, the number of the particles of the positive electrode active material meeting a/b≥3 is N, where N≥2.