Lithium Secondary Battery Electrode Mix for Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries with Si-based negative electrodes and lithium NCM (A) oxide positive electrodes suffer from inferior thermal stability and rapid capacity drop, making them unsuitable for high-energy density applications.
Innovation Solution
A lithium secondary battery design that includes a negative electrode with a silicon-based active material and a positive electrode composed of a mixture of a layered active material containing nickel and an olivine-based active material, with specific weight ratios of olivine-based active material (A) and silicon-based active material (B) satisfying Formulas 1 and 2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Si-based negative electrode material is used to increase capacity, then energy density is improved, but thermal stability deteriorates
Solution Approach 1:
The patent uses a composite negative electrode structure where Si-based active material particles are embedded in a carbon matrix. This composite approach allows the Si-based material to provide high capacity while the carbon matrix suppresses volume expansion and maintains thermal stability, resolving the contradiction between energy density improvement and thermal stability deterioration.
Solution Approach 2:
The patent employs a carbon coating layer as a flexible shell around the Si-based active material particles. This thin film structure accommodates volume changes during lithium insertion/extraction while maintaining structural integrity and thermal stability, allowing the system to achieve high energy density without sacrificing safety.
2Use of energy by moving object
If Si-based negative electrode material is used to increase capacity, then energy density is improved, but life performance deteriorates due to volume expansion
Solution Approach 1:
The carbon coating layer acts as a flexible shell that expands and contracts with the Si-based particles during cycling. This flexible enclosure maintains electrical contact and prevents particle disconnection, thereby preserving life performance while enabling high energy density through Si-based material utilization.
Solution Approach 2:
The carbon matrix serves as an intermediary between the Si-based active material and the electrolyte, mediating the volume expansion effects. It provides a stable conductive network that maintains electrical connectivity during volume changes, preventing conductive path disconnection and maintaining long-term cycling stability.
3Use of energy by moving object
If lithium NCM (A) oxide positive electrode is used with Si-based negative electrode for high capacity, then energy density is improved, but thermal stability deteriorates
Solution Approach 1:
The patent creates a composite electrode system where the Si-based negative electrode is paired with a carefully designed positive electrode composition. The overall battery system achieves high energy density through the high-capacity Si-based negative electrode while the positive electrode composition and electrolyte formulation work together to suppress thermal runaway, resolving the contradiction between energy density and thermal 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
This configuration simultaneously secures high energy density, thermal stability, and superior life performance, addressing the previously incompatible requirements of energy density and thermal stability.
Implementation Method 1
During charging, the lithium ions intercalated to the positive electrode move to the negative electrode through the electrolyte solution
Implementation Method 2
During discharging, the lithium ions move back to the positive electrode from the negative electrode
Data Source
AI summary
Disclosed is a lithium secondary battery including: a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode comprises a positive electrode active material layer comprising a positive electrode active material layer composition, wherein the negative electrode comprises a negative electrode active material layer comprising a negative electrode active material layer composition, wherein the positive electrode active material layer composition comprises a positive electrode active material comprising a layered active material containing nickel, and an olivine-based active material, wherein the negative electrode active material layer composition comprises a negative electrode active material comprising a silicon-based active material, and wherein a part by weight of the olivine-based active material (A) based on 100 parts by weight of the positive electrode active material, and a part by weight of the silicon-based active material (B) based on 100 parts by weight of the negative electrode active material satisfy Formulas 1 and 2:4.524+0.939×e0.0537×A<B<-4.312+5.183×e0.0537×A[Equation 1]10≤A≤90.[Equation 2]