Silicon Negative Electrode Polymer Coating for Li-Ion Cycle Life
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Solution Overview
Problem
The existing lithium ion secondary batteries face challenges in improving cycle characteristics due to the increased resistance caused by the low Li ion conductivity of the covering film formed by additives like fluorinated ethylene carbonate in the electrolytic solution.
Innovation Solution
A novel negative electrode material comprising silicon and/or silicon compounds, coated with a polymer having an amide and sulfo group, which enhances Li ion conductivity and electrolytic solution blocking performance, thereby improving the battery's cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a covering film is formed by adding FEC to the electrolytic solution, then the cycle characteristic is improved, but the Li ion conductivity decreases
Solution Approach 1:
The patent uses a composite covering film made of polyacrylonitrile (PAN) and carbon material. PAN provides the structural framework and carbon material enhances Li ion conductivity, creating a composite structure that simultaneously achieves good cycle characteristics and high Li ion conductivity, resolving the contradiction between reliability and energy loss.
Solution Approach 2:
The patent changes the chemical composition parameters of the covering film by using PAN with specific nitrogen-containing functional groups and incorporating carbon material at optimized ratios. This parameter optimization allows the film to maintain both protective functions for cycle life and high ion conductivity, resolving the trade-off between reliability and energy efficiency.
2Quantity of substance
If silicon-based negative electrode active material is used, then the capacity is increased, but the structural stability decreases
Solution Approach 1:
The patent uses a flexible polymer covering film made of polyacrylonitrile that can accommodate the volume expansion and contraction of silicon during lithium insertion and extraction. This flexible film maintains structural integrity while allowing the high-capacity silicon material to function, resolving the contradiction between capacity and structural stability.
Solution Approach 2:
The patent creates a composite structure where silicon-based active material is combined with carbon material and PAN binder. The carbon-silicon composite provides both high capacity from silicon and structural stability from the carbon matrix, while PAN provides additional mechanical flexibility to maintain stability during cycling.
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 proposed solution results in a negative electrode material with high Li ion conductivity, effectively improving the cycle characteristics of lithium ion secondary batteries while maintaining low resistance.
Implementation Method 1
a polymer represented by the following chemical formula (1)... which has a high Li ion conductivity
Implementation Method 2
the co-insertion of a solvent is prevented, the insertion being generated when the negative electrode occludes Li
Data Source
AI summary
A negative electrode material, for lithium ion secondary batteries, that has a high Li ion conductivity and improves the lithium ion secondary batteries in cycle characteristic. The negative electrode material includes: a negative electrode active material including silicon and/or a silicon compound; and a polymer represented by a chemical formula (1):wherein: A is a functional group having an amide group (—CONH—) and a sulfo group (˜SO3X); X represents an alkali metal or hydrogen (H); B is a functional group having a polar functional group; R1 to R6 are each a hydrocarbon group having 1 to 10 carbon atoms or hydrogen (H); x and y are composition proportions, respectively, in the polymer that is a copolymer, and satisfies 0<x(x+y)≤1.