Alloy-Composite Negative Electrode for Li-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, leading to cracking and loss of electron conductivity, which limits their cycle life and capacity retention.
Innovation Solution
A negative electrode active material comprising a carbonaceous powder material with a specific Raman spectrum peak intensity ratio and an alloy phase that undergoes thermoelastic diffusionless transformation, mitigating strain and improving discharge capacity and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If alloy-based negative electrode active materials (Si or Sn) are used to achieve higher capacity, then discharge capacity per mass is improved, but volume expansion/contraction during charging/discharging causes cracking and capacity deterioration
Solution Approach 1:
The invention uses a composite material system consisting of alloy particles (Si or Sn) combined with a specific binder material. The binder material forms a matrix that encapsulates the alloy particles, creating a composite structure that maintains the high capacity benefits of the alloy while mitigating the volume expansion/contraction problem through the binder's mechanical properties and volume change compensation capability.
Solution Approach 2:
The invention changes the physical and chemical parameters of the negative electrode by introducing a binder material with specific properties (carbonaceous material with controlled graphitization degree, specific Raman spectrum characteristics). This parameter change transforms the electrode structure from pure alloy particles to a composite system where the binder's volume change characteristics compensate for the alloy's expansion/contraction, improving cycle stability.
2Reliability
If graphite-based negative electrode active materials are used, then volume stability is maintained, but discharge capacity per mass is limited
Solution Approach 1:
The invention creates a composite negative electrode active material that combines alloy particles (providing high capacity) with binder material (providing volume stability). This composite structure allows the electrode to achieve discharge capacity per mass exceeding that of conventional graphite while maintaining volume stability through the binder's mechanical support and volume change compensation.
Solution Approach 2:
The invention applies different material properties to different components of the negative electrode: alloy particles provide high capacity in specific regions, while the binder material provides volume stability and structural support in the matrix. This local differentiation of material qualities allows the overall electrode to achieve both high capacity and volume stability simultaneously.
3Quantity of substance
If Si or Sn single substance is used, then discharge capacity per mass is significantly improved, but volume expansion/contraction ratio reaches about 400% causing cracking
Solution Approach 1:
The invention forms a composite where alloy particles (Si or Sn) are embedded in a binder material matrix. The binder material's volume change characteristics are specifically selected to compensate for the 400% volume expansion/contraction of the alloy particles, maintaining overall electrode shape stability while preserving the high capacity benefits of the alloy.
Solution Approach 2:
The binder material acts as an intermediary between the alloy particles and the electrode structure. It mediates the volume expansion/contraction by providing a compliant matrix that absorbs and distributes the mechanical stress, preventing direct cracking of the alloy particles and maintaining electrical connectivity throughout charge-discharge cycles.
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 material enhances discharge capacity per mass, cycle life, and reduces irreversible capacity by relaxing strain through thermoelastic diffusionless transformation, resulting in improved performance compared to conventional alloy-based and graphite-based materials.
Implementation Method 1
Material C: powder material whose main component is an active substance made up of an alloy phase. This alloy phase undergoes thermoelastic diffusionless transformation when releasing metal ions or occluding the metal ions.
Implementation Method 2
the negative electrode material of Patent Literature 1 includes a Ti-Ni superelastic alloy, and Si particles formed in the superelastic alloy
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2E
AI summary
Provided is a negative electrode active material which can improve discharge capacity per amount and charge-discharge cycle characteristics. The negative electrode active material of the present embodiment contains at least one of material A and material B, and material C: Material A: carbonaceous powder material in which a ratio of a peak intensity at 1360 cm-1 with respect to a peak intensity at 1580 cm-1 in the Raman spectrum is not more than 0.5; Material B: carbonaceous powder material in which a ratio of a peak intensity at 1360 cm-1 with respect to a peak intensity at 1580 cm-1 in the Raman spectrum is more than 0.5; Material C: powder material whose main component is an active substance made up of an alloy phase. This alloy phase undergoes thermoelastic diffusionless transformation when releasing metal ions or occluding the metal ions.