Carbon-Coated Silicon-Lithium Silicate Anode for Expansion Control
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Solution Overview
Problem
Existing lithium ion battery negative electrode materials face challenges in achieving high specific capacity, high first coulombic efficiency, and good cycle stability due to limitations in graphite and silicon-based materials, with silicon experiencing volume expansion and lithium silicate being chemically inert.
Innovation Solution
A composite negative electrode material comprising lithium silicate, silicon oxide, an activator, and a carbon coating is developed, where the activator enhances conductivity and supports the lithium silicate structure, and the carbon coating alleviates volume expansion, resulting in improved electrochemical properties and cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode, then specific capacity is improved (theoretical capacity up to 4200 mAh/g), but volume expansion occurs (up to 300%) leading to poor cycle performance
Solution Approach 1:
Silicon particles are embedded inside lithium silicate matrix, forming a nested structure where the inner silicon provides high capacity while the outer lithium silicate shell constrains volume expansion and maintains structural integrity during cycling
Solution Approach 2:
The negative electrode uses a composite material system consisting of lithium silicate, silicon oxide, activator, and carbon coating, combining the high capacity of silicon with the structural stability of lithium silicate and the protective properties of carbon
2Reliability
If lithium silicate is used as negative electrode material, then cycle performance is improved, but first coulombic efficiency is reduced due to electrochemical inertness
Solution Approach 1:
An activator component is introduced as an intermediary substance that facilitates lithium ion insertion into and extraction from lithium silicate, overcoming its electrochemical inertness and enabling reversible capacity while maintaining cycle stability
Solution Approach 2:
The carbon coating is applied selectively on the surface of lithium silicate particles, providing localized electrochemical activity and conductivity enhancement where lithium ion transfer occurs, while the bulk lithium silicate maintains its structural stability
3Reliability
If graphite is used as negative electrode material, then cycle stability is maintained, but specific capacity is limited (theoretical capacity only 372 mAh/g)
Solution Approach 1:
The invention creates a composite negative electrode material that combines silicon (high capacity) with lithium silicate and carbon (structural stability), achieving both high specific capacity and good cycle stability that neither material can provide alone
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 composite material achieves a first coulombic efficiency of no less than 83.6% and a 50-cycle capacity retention rate of no less than 82% at 0.1 C current density, with a first discharging specific capacity of no less than 1263 mAh/g, addressing the limitations of existing materials.
Implementation Method 1
the carbon coating outside the composite matrix material... may further alleviate the problem of volume expansion of silicon and silicon oxide in the charging and discharging process
Implementation Method 2
The activator in the composite matrix material of the present disclosure, on one hand, may improve the conductivity of the material, and further enhance the electrochemical property of the negative electrode material
Implementation Method 3
lithium ions have a sufficient space to be separated from and embedded into the structure, and further show certain reversible capacity
Data Source
AI summary
A negative electrode material includes a composite matrix material and a carbon coating coated on the composite matrix material. The composite matrix material includes lithium silicate, silicon oxide, an activator, and silicon embedded in the lithium silicate and the silicon oxide.