LMFP Cathode Composition Balancing SEI Lithium Loss in Li-Ion Batteries
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Solution Overview
Problem
Lithium manganese iron phosphate (LMFP) positive electrode material in lithium ion batteries faces reduced actual specific capacity due to lithium consumption in forming the SEI film during charge and discharge, limiting the battery's capacity exertion.
Innovation Solution
A lithium ion battery design incorporating a positive electrode sheet with lithium manganese iron phosphate and a ternary material, along with a graphite negative electrode sheet, where the materials are balanced to meet specific capacity and efficiency ratios, enhancing the battery's energy density and cycle performance while ensuring safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium manganese iron phosphate is used as positive electrode material to achieve high theoretical specific capacity, then the initial efficiency and theoretical capacity are improved, but the actual specific capacity is reduced due to lithium consumption in SEI film formation
Solution Approach 1:
The patent changes the chemical composition parameters of the positive electrode material by introducing a ternary material (LiNiaCo1-b- aMn1-cXcO2) with specific element ratios and oxidation states. This compositional parameter adjustment creates a synergistic effect that improves actual capacity while maintaining theoretical capacity potential
Solution Approach 2:
The patent creates a composite positive electrode material system combining lithium manganese iron phosphate (LMFP) with a ternary material. This composite structure leverages the high capacity of LMFP and the stability/low cost of ternary materials, achieving both high theoretical and actual specific capacity through material synergy
2Ease of manufacture
If graphite negative electrode is used to form SEI film during charge-discharge, then the battery structure is simplified and manufacturing is easier, but active lithium is consumed reducing the capacity exertion of lithium manganese iron phosphate
Solution Approach 1:
The patent adjusts the capacity ratio parameter between positive and negative electrodes by incorporating ternary material with different lithium content and electrochemical properties. This parameter change optimizes the lithium balance, ensuring sufficient active lithium remains after SEI formation to achieve high capacity exertion of LMFP
Solution Approach 2:
The patent uses the well-established graphite negative electrode structure (copying proven design) but compensates for its lithium consumption drawback through positive electrode material optimization, thereby maintaining manufacturing simplicity while achieving high capacity
3Quantity of substance
If lithium manganese iron phosphate is used to provide higher capacity, then the energy density is improved, but the structural stability and cycle performance may be compromised
Solution Approach 1:
The patent creates a composite where LMFP provides high capacity and the ternary material provides structural stability. The ternary material's robust layered structure acts as a stabilizing framework that maintains overall composition stability during cycling while allowing LMFP to contribute its high capacity
Solution Approach 2:
The patent assigns different functional qualities to different materials in the composite: LMFP is optimized for high capacity contribution while the ternary material is optimized for structural stability and cost-effectiveness. This local quality differentiation allows the system to achieve both high capacity and structural stability
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 balanced mixture of LMFP and ternary material improves the actual specific capacity and energy density of the lithium ion battery, maintaining safety and cycle performance, with reduced Mn dissolution after 2000 charge-discharge cycles.
Implementation Method 1
The positive electrode active material of the positive electrode sheet includes lithium manganese iron phosphate and a ternary material. The negative electrode active material of the negative electrode sheet is graphite.
Implementation Method 2
the graphite negative electrode active material of lithium ion battery forms an SEI film during the charge and discharge process, and active lithium from lithium manganese iron phosphate is consumed in the SEI film forming process
Data Source
AI summary
A positive electrode active material of a lithium ion battery includes lithium manganese iron phosphate and a ternary material. A negative electrode active material is graphite. The lithium ion battery meets the following formulas:1.08≤M3*η3*y/M1*η1*A1+M2*η2*A2*x≤1.12 and0.49≤M1*1- η1*A1+M2*1 -η2*A2*x/M3*1 -η3*y≤1.15where M1 is the first-charge specific capacity of lithium manganese iron phosphate; η1, is the initial efficiency of lithium manganese iron phosphate; A1 is the percent by mass of lithium manganese iron phosphate in the positive electrode active material; M2 is the first-charge specific capacity of the ternary material; η2 is the initial efficiency of the ternary material; A2 is the percent by mass of the ternary material in the positive electrode active material; M3 is the first-discharge specific capacity of graphite; η3 is the initial efficiency of graphite; and x and y are the coating amounts of the positive electrode active material and the negative electrode active material, respectively.