Si-Zr and Sn-X Anode Material for Li-Ion Cycle Stability
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Solution Overview
Problem
Lithium-ion batteries using silicon as a negative electrode active material face challenges with cycle characteristics and initial discharging capacity due to volume expansion and contraction, leading to particle cracking and reduced Li-ion diffusion paths.
Innovation Solution
A negative electrode active material comprising a Si phase, a Si—Zr compound phase, and a Sn—X compound phase, where X is Cu, Ti, Co, Fe, or Zr, with specific mass proportions to balance capacity retention and initial coulombic efficiency, ensuring effective stress absorption and enhanced Li-ion diffusivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si is used as negative electrode active material to achieve high capacity, then capacity is improved, but cycle characteristics deteriorate due to volume expansion and contraction causing particle cracking
Solution Approach 1:
The patent uses a composite material system consisting of Si phase, Si-Zr compound phase, and Sn-X compound phase. The Si-Zr compound phase forms an island structure that absorbs expansion stress, while the Sn-X compound phase provides structural support. This composite structure allows Si to maintain high capacity while the surrounding compound phases prevent particle cracking and maintain cycle characteristics.
Solution Approach 2:
The patent creates different local structures within the material: Si phase regions provide high capacity, Si-Zr compound phase regions absorb expansion stress, and Sn-X compound phase regions maintain structural integrity. Each phase has a specific local function that contributes to the overall performance, resolving the contradiction between capacity and cycle characteristics.
2Reliability
If Si is miniaturized to improve cycle characteristics, then particle stability is improved, but initial discharging capacity and initial coulombic efficiency decrease due to reduced Li-ion diffusion paths
Solution Approach 1:
The Sn-X compound phase acts as an intermediary that facilitates Li-ion diffusion. It forms a stable structural framework that provides efficient diffusion paths for Li-ions to reach the Si phase, compensating for the reduced diffusion paths caused by miniaturization. This intermediary structure maintains both cycle characteristics and initial discharging capacity.
3Reliability
If alloying elements are added to Si to prevent particle collapse, then cycle characteristics are improved, but Li-ion diffusion paths are reduced
Solution Approach 1:
The patent creates distinct functional zones: Si-Zr compound phase regions specifically for stress absorption and structural stability, and Sn-X compound phase regions specifically for providing Li-ion diffusion paths. By separating these functions into different local regions, the patent achieves both particle stability and efficient Li-ion diffusion, resolving the contradiction between cycle characteristics and initial coulombic efficiency.
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 improves cycle characteristics, initial discharging capacity, and initial coulombic efficiency by minimizing particle collapse and maintaining a stable Li-ion diffusion path, achieving a good balance between capacity retention and efficiency.
Implementation Method 1
since Si stores the Li-ions by an alloying reaction with Li, large volume expansion and contraction occur accompanying with the storing and releasing of the Li-ions
Implementation Method 2
a Si-Zr compound phase forms into an island form and a Si phase forms into a sea form in a process of cooling and solidifying a molten alloy. Since many parts of the sea-form Si phase are located on an outermost surface, a stress applied to the Si-Zr compound phase is small during expansion of the Si phase, and collapse of particles can be prevented
Implementation Method 3
even when the cycle characteristics are improved by miniaturizing the Si phase, it is possible to prevent reductions in an initial discharging capacity and in an initial coulomb efficiency
Data Source
AI summary
The present invention relates to a negative electrode active material for a lithium-ion battery, containing a Si phase, a Si—Zr compound phase, and a Sn—X compound phase in which X is at least one element selected from the group consisting of Cu, Ti, Co, Fe, Ni, and Zr, the Sn—X compound phase has a proportion of 0.1 mass % to 18 mass % to the whole, and the Si phase has a proportion of 10 mass % to 80 mass % to the whole.