Metal Phosphate Particle Size Optimization for Battery Electrodes
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Solution Overview
Problem
Lithium ion secondary batteries with high-potential positive electrode active materials face issues of increased operating voltage leading to electrolyte decomposition, transition metal elution, and subsequent capacity retention decrease, while existing solutions like trilithium phosphate, although effective, can increase internal resistance due to low conductivity of the formed film.
Innovation Solution
A method involving a positive electrode paste with a mixture of first and second metal phosphate particles of different sizes, where the second particles are larger than the first by 1.3 μm or more, to improve conductivity and dispersibility, forming a protective film that reduces internal resistance and functions as an acid consumer, thereby maintaining capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high-potential positive electrode active material is used to increase operating voltage, then the battery output and capacity are improved, but the electrolyte decomposes and transition metal elutes during charging and discharging
Solution Approach 1:
Metal phosphate particles are introduced as an intermediary substance between the high-potential positive electrode active material and the electrolyte. These particles form a protective film that mediates the interaction, preventing direct contact and harmful reactions while allowing ionic transport, thus resolving the contradiction between high voltage operation and electrolyte stability
Solution Approach 2:
The metal phosphate particles perform preliminary protective action by forming a stable film on the positive electrode active material surface before the electrolyte can decompose or cause transition metal elution. This preemptive protection prevents the harmful effects that would otherwise occur during high-voltage charging and discharging
2Reliability
If trilithium phosphate is added to prevent transition metal elution, then capacity retention is improved, but internal resistance increases due to low conductivity of the formed film
Solution Approach 1:
The invention changes the particle size parameter of the metal phosphate additive, using particles with a specific size range (0.1 μm to 1.0 μm, preferably 0.3 μm to 0.8 μm). This parameter optimization allows the formation of a protective film with sufficient conductivity while maintaining the acid-consuming function, thus resolving the contradiction between capacity retention and internal resistance
Solution Approach 2:
The metal phosphate particles are distributed locally throughout the positive electrode active material layer, creating localized protective zones. This local distribution ensures that the protective function is maintained throughout the electrode while the optimized particle size ensures sufficient conductivity in each local region, preventing excessive internal resistance
3Object-affected harmful factors
If metal phosphate particles are reduced in size to improve film conductivity, then internal resistance decreases, but manufacturing cost increases
Solution Approach 1:
The invention optimizes the particle size parameter to a specific range (0.1 μm to 1.0 μm, preferably 0.3 μm to 0.8 μm) that balances conductivity improvement with manufacturing cost. This parameter optimization ensures sufficient film conductivity while avoiding the need for expensive ultra-fine particle processing, thus resolving the contradiction between internal resistance and manufacturing cost
Solution Approach 2:
The metal phosphate particles maintain continuous protective function across the positive electrode active material surface. The optimized particle size ensures continuous film formation with adequate conductivity while maintaining cost-effectiveness, as the particles are small enough to provide uniform coverage but not so small as to require expensive manufacturing processes
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 approach results in a nonaqueous electrolyte secondary battery with reduced internal resistance and manufacturing cost, as the smaller particles enhance film conductivity and the larger particles effectively function as acid consumers without affecting cost, ensuring low internal resistance and prolonged battery life.
Implementation Method 1
trilithium phosphate can function as an acid consuming material by reacting with hydrofluoric acid (HF) produced in an electrolytic solution
Implementation Method 2
the smaller particles enhance film conductivity and the larger particles effectively function as acid consumers
Data Source
AI summary
A method of manufacturing a nonaqueous electrolyte secondary battery includes a positive electrode paste preparation step, a positive electrode sheet preparation step, a construction step, and an initial charging step. In the positive electrode paste preparation step, a positive electrode paste is prepared by dispersing a positive electrode active material, a binder, and a metal phosphate in a solvent. The metal phosphate includes a first metal phosphate and a second metal phosphate having an average particle size which is more than that of the particles of the first metal phosphate by 1.3 μm or more.