LFP Positive Electrode Composition for High-Loading Conductive Paths
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Solution Overview
Problem
Conventional lithium ion secondary battery compositions using carbon black and carbon nanotubes struggle to achieve high energy density and excellent cycle characteristics, particularly when using lithium iron phosphate as the active material, due to insufficient conductive path formation and excessive use of conductive materials.
Innovation Solution
A specific combination of carbon black with small particle size and long structure, and carbon nanotubes with small fiber diameter and limited BET specific surface area, is used in conjunction with lithium iron phosphate to enhance energy density and cycle characteristics, with the lithium iron phosphate content being 95% or more by mass, and the carbon nanotubes having an average diameter of 10 nm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon black and carbon nanotubes are used in conventional amounts to form conductive paths, then conductivity is improved, but the amount of active material must be reduced
Solution Approach 1:
The patent changes the physical parameters of carbon black (using smaller particle sizes of 10nm or less and controlling DBP absorption to 200-400mL/100g) to improve its conductive efficiency. This allows forming effective conductive paths with smaller amounts of carbon black, thereby increasing active material content while maintaining conductivity.
Solution Approach 2:
The patent creates a composite conductive system combining carbon black with specific properties (small particle size, controlled structure) and carbon nanotubes. This composite approach synergistically improves conductive path formation efficiency, allowing reduced total conductive material content while maintaining or enhancing conductivity.
2Ease of manufacture
If carbon black with large particle size is used, then manufacturing is easier, but conductive path formation is insufficient
Solution Approach 1:
The patent changes the particle size parameter of carbon black to 10nm or less, which fundamentally improves conductive path formation capability. The smaller particle size allows carbon black to more effectively bridge active material particles and form continuous conductive networks, resolving the contradiction between particle size and conductive performance.
3Reliability
If thick carbon fiber is used to prepare sufficient conductive path, then conductivity is improved, but electrolyte retention around active material becomes insufficient
Solution Approach 1:
The patent changes from using thick carbon fiber to using carbon black with particle size of 10nm or less. The smaller particle size of carbon black allows it to disperse more uniformly around active material particles, maintaining conductive paths while leaving sufficient space for electrolyte retention, thus resolving the contradiction between conductivity and electrolyte access.
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 composition results in a lithium ion secondary battery with high energy density, low internal resistance, and excellent output and cycle characteristics, even at low temperatures, by optimizing the conductive path and electrolyte retention.
Implementation Method 1
The carbon black has a common 'structure' in which approximately spherical primary particles are connected like a rosary. The length of the structure can be indirectly evaluated by using the DBP absorption amount measured according to the method of JIS K 6217-4:2017. Generally, the larger the DBP absorption amount, the longer the structure. The longer structure exerts good electric conductivity
Implementation Method 2
The longer structure exerts good electric conductivity and liquid retention, which is the ability to hold a non-aqueous electrolyte
Data Source
AI summary
A composition for a positive electrode of a lithium ion secondary battery, the composition comprising: an active material capable of storing and extracting lithium ion; and an electric conductive material, wherein the active material is lithium iron phosphate, wherein the conductive material includes carbon black and carbon nanotube, wherein the carbon black has an average primary particle diameter of 39 nm or less, and wherein the carbon nanotube has an average diameter of 20 nm or less.