Alloy-Ceramic Composite Negative Electrode for Lithium-Ion Batteries
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Solution Overview
Problem
Graphite-based negative electrode active materials in lithium-ion batteries face challenges with capacity deterioration due to significant volume expansion and contraction during charging and discharging, leading to cracking and loss of electron conductivity.
Innovation Solution
A negative electrode active material comprising an alloy phase that undergoes thermoelastic diffusionless transformation, combined with ceramics dispersion, to mitigate strain and improve cycle characteristics and discharge capacity per volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If alloy-based negative electrode active materials (Si or Sn) are used to increase capacity, then the discharge capacity per volume is improved, but the charge-discharge cycle characteristics deteriorate due to large volume expansion/contraction
Solution Approach 1:
The invention changes the crystal structure parameter of the alloy phase by inducing a thermoelastic diffusionless transformation from a disordered state to an ordered state. This transformation alters the volume expansion/contraction characteristics of the alloy during lithium ion occlusion/release cycles, reducing the mechanical stress and preventing cracking, thereby improving charge-discharge cycle characteristics while maintaining high discharge capacity per volume
Solution Approach 2:
The invention utilizes phase transition by inducing a thermoelastic diffusionless transformation (martensitic transformation) in the alloy phase. The alloy transforms from a disordered crystal structure to an ordered crystal structure during charging/discharging cycles. This phase transition enables the material to accommodate volume changes elastically, suppressing crack propagation and improving cycle stability while preserving high capacity
2Quantity of substance
If Si single substance or Sn single substance is used as negative electrode material, then the discharge capacity per volume is significantly improved compared to graphite, but cracking occurs due to volume expansion/contraction ratio of about 400%
Solution Approach 1:
The invention changes the crystal structure parameter of the alloy phase through thermoelastic diffusionless transformation, transitioning from a disordered to an ordered state. This transformation fundamentally alters the volume expansion/contraction behavior, reducing it from approximately 400% in single-substance Si or Sn to a much smaller range that preserves structural integrity while maintaining high discharge capacity per volume
Solution Approach 2:
The invention creates a composite structure where the alloy phase exists in two crystallographic states (disordered and ordered) that can transform reversibly. This composite approach combines the high capacity benefits of Si or Sn with the structural stability of a transformation-capable crystal system, preventing cracking while maximizing discharge capacity per volume
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 solution enhances the volumetric discharge capacity and charge-discharge cycle characteristics of lithium-ion batteries by relaxing strain through thermoelastic diffusionless transformation and suppressing crack propagation with ceramic dispersion, resulting in improved capacity retention ratios.
Implementation Method 1
an alloy phase which undergoes thermoelastic diffusionless transformation when releasing metal ions which are occluded, or occluding metal ions
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2E
AI summary
Provided is a negative electrode active material that can improve the discharge capacity per volume and/or charge-discharge cycle characteristics. The negative electrode active material according to the present embodiment contains an alloy phase and ceramics. The alloy phase undergoes thermoelastic diffusionless transformation when releasing or occluding metal ions. The ceramics is dispersed in the metal phase. The content of ceramics in the alloy phase is more than 0 to 50 mass% with respect to the total mass of the alloy phase and the ceramics.