Alloy Negative Electrode Active Material for Lithium-Ion Batteries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Graphite-based negative electrode active materials in lithium-ion batteries face challenges such as limited capacity and short service life 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 with a specific alloy phase that undergoes thermoelastic diffusionless transformation, composed of elements like Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, and C, with a crystal structure that transforms from DO3 to 2H and back, mitigating strain through reversible transformations.
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 capacity is improved, but the volume expansion/contraction rate increases significantly causing cracking and capacity deterioration
Solution Approach 1:
The invention changes the crystal structure parameter of the alloy phase from a non-transforming structure to a thermoelastic diffusionless transformation-capable structure (DO3 ↔ 2H). This parameter change enables the alloy to undergo reversible structural transformation during charging/discharging, accommodating volume changes without cracking, thus maintaining both high capacity and good cycle characteristics.
Solution Approach 2:
The invention utilizes phase transition by selecting alloy phases that undergo thermoelastic diffusionless transformation between DO3 and 2H crystal structures. This phase transition occurs reversibly during charging and discharging, allowing the material to adapt to volume changes while maintaining structural integrity and preventing crack formation.
2Quantity of substance
If Si or Sn single substance is used as negative electrode active material, then the capacity is improved, but the volume expansion/contraction rate reaches about 400% causing significant cracking
Solution Approach 1:
The invention creates a composite alloy phase containing multiple elements (Cu, Sn, and at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, B, or C) that undergoes thermoelastic diffusionless transformation. This composite structure combines the high capacity benefits of Sn/Si with the structural stability provided by the transformation-capable alloy phase, preventing crack formation even at high capacity levels.
3Reliability
If graphite-based negative electrode active materials are used, then the structural stability is maintained, but the capacity is limited and service life is short
Solution Approach 1:
The invention changes the material parameter from graphite (low capacity, stable structure) to a transformation-capable alloy phase (high capacity, adaptive structure). The key parameter change is the introduction of thermoelastic diffusionless transformation capability, which allows the high-capacity alloy to maintain structural stability through reversible phase transitions during cycling.
4Quantity of substance
If alloy phase undergoes volume expansion/contraction during charging/discharging, then the capacity is improved, but strain accumulates causing cracking and loss of electron conductivity
Solution Approach 1:
The invention utilizes phase transition to convert harmful strain into a beneficial reversible structural change. The thermoelastic diffusionless transformation between DO3 and 2H phases occurs in response to charging/discharging-induced strain, accommodating volume changes reversibly without accumulating damage, thus preventing crack formation and maintaining electron conductivity.
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 from volume changes, resulting in improved capacity retention and cycle stability.
Implementation Method 1
the alloy phase undergoes thermoelastic diffusionless transformation either when releasing metal ions, or when occluding the metal ions
Data Source
Figure 1
Figure 2
Figure 3(a)~3(i)
AI summary
Provided is a negative electrode active material that can improve the capacity per volume and charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery. The negative electrode active material according to the present embodiment contains an alloy phase. The alloy phase undergoes thermoelastic diffusionless transformation when releasing or occluding metal ions. The negative electrode active material of the present embodiment is used in a nonaqueous electrolyte secondary battery. Thermoelastic diffusionless transformation refers to so-called thermoelastic martensitic transformation.