Olivine Cathode Conductive Network for High-Current Battery Performance
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries using olivine-type lithium-containing metal phosphate as the positive electrode active material face challenges with high electrical resistance, leading to poor discharge performance and charge-discharge cycle performance at high current discharge, due to the high resistance overvoltage and low battery voltage, as well as issues with conductive agent distribution and volumetric changes.
Innovation Solution
Incorporating a mixture of lumped carbon particles and carbon fiber as the conductive agent in the positive electrode mixture layer, along with reducing the particle size of the olivine-type lithium-containing metal phosphate to shorten the lithium diffusion path, helps form stable conductive paths and reduce electrical resistance, while the carbon fiber aids in heat dissipation and maintaining conductive paths during volumetric changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If olivine-type lithium-containing metal phosphate is used as the positive electrode active material, then manufacturing cost is reduced and resource stability is improved, but electrical resistance increases leading to poor discharge performance at high current
Solution Approach 1:
The patent uses a composite material consisting of olivine-type lithium-containing metal phosphate particles combined with conductive carbon materials. This composite structure maintains the cost advantages of the phosphate material while the carbon component provides enhanced electrical conductivity, resolving the contradiction between manufacturing cost and discharge performance.
Solution Approach 2:
The patent applies conductive agents specifically to the surface and interfaces of the phosphate particles, creating local regions of high conductivity where electron transfer occurs. This localized enhancement of electrical properties allows the bulk material to maintain its cost-effective composition while achieving improved overall conductivity for better discharge performance.
2Reliability
If the amount of conductive agent is increased to reduce electrical resistance, then electrical resistance decreases, but the relative proportion of positive electrode active material reduces leading to insufficient battery capacity
Solution Approach 1:
The patent optimizes the particle size of the phosphate material to sub-micron dimensions, which dramatically increases the surface area to volume ratio. This parameter change allows conductive agents to be more effectively distributed and utilized, achieving low electrical resistance with minimal conductive agent content, thereby preserving battery capacity.
Solution Approach 2:
The patent creates a synergistic composite where conductive carbon materials are intimately mixed with phosphate particles at optimized ratios. This composite structure provides efficient conductive networks throughout the electrode, achieving low resistance without requiring excessive conductive agent that would compromise active material content and capacity.
3Reliability
If lumped carbon is used as the conductive agent, then electrical resistance is reduced, but the positive electrode shows large volumetric change after initial charge-discharge causing conductive path disconnection
Solution Approach 1:
The patent employs fine carbon particles that can flexibly conform to the volumetric changes of the phosphate particles during charge-discharge cycling. These flexible carbon components maintain continuous conductive paths despite the expansion and contraction of the active material, preventing disconnection while providing necessary conductivity.
Solution Approach 2:
The patent uses carbon particles as an intermediary material that bridges the phosphate particles and accommodates their volumetric changes. This intermediary carbon phase absorbs the mechanical stress of expansion/contraction while maintaining electrical connectivity, acting as a buffer that preserves conductive paths throughout cycling.
4Reliability
If particle size of lithium-containing metal phosphate is reduced to increase contact area, then electrical resistance decreases, but lithium diffusion path becomes shorter which should improve performance however charge-discharge cycle performance still deteriorates at high current
Solution Approach 1:
The patent combines fine phosphate particles with conductive carbon materials to create a composite structure where the carbon phase provides stable conductive networks that persist throughout cycling. This composite approach addresses the cycle performance deterioration by maintaining electrical connectivity even as the fine particles undergo repeated volume changes during high current charge-discharge operations.
Solution Approach 2:
The conductive carbon material acts as an intermediary that stabilizes the electrode structure during cycling. It provides a robust conductive framework that accommodates the volumetric changes of the fine phosphate particles, preventing particle aggregation and maintaining electrical contact over many cycles, thereby improving charge-discharge cycle performance.
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 approach significantly improves discharge performance and charge-discharge cycle performance at high current discharge by reducing electrical resistance and preventing conductive path disconnection, leading to enhanced output power characteristics and capacity retention.
Implementation Method 1
Incorporating a mixture of lumped carbon particles and carbon fiber as the conductive agent in the positive electrode mixture layer helps form stable conductive paths and reduce electrical resistance
Implementation Method 2
the carbon fiber aids in heat dissipation and maintaining conductive paths during volumetric changes
Implementation Method 3
Non-aqueous electrolyte secondary batteries typically use a non-aqueous electrolyte and perform charge-discharge operations by transferring lithium ions between the positive electrode and the negative electrode
Data Source
AI summary
A non-aqueous electrolyte secondary battery has a positive electrode (1), a negative electrode (2), and a non-aqueous electrolyte. The positive electrode has a positive electrode mixture layer containing a positive electrode active material, a binder agent, and a conductive agent. The positive electrode active material in the positive electrode mixture layer contains an olivine-type lithium-containing metal phosphate represented by the general formula LixMPO4, where M is at least one element selected from the group consisting of Co, Ni, Mn, and Fe, and x is 0<x<1.3. The conductive agent in the positive electrode mixture layer is composed of a mixture of carbon particles and carbon fiber.