Silicon-Based Alloy Negative Electrode for Lithium Battery
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Solution Overview
Problem
Current negative active materials for lithium batteries, such as Si and Sn, suffer from volumetric expansion during charging and discharging, leading to degraded capacity despite research into various alloys and complexes.
Innovation Solution
A silicon-based alloy with a composition of Si, Ti, and Fe, including an inactive matrix with Ti2Ni and NiSi2 phases, and active silicon nanoparticles dispersed within, is developed to improve discharge capacity and lifetime characteristics by controlling the Fe content and particle size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-carbonaceous materials such as Si and Sn are used as negative active material, then capacity is improved (about 10 times greater than graphite), but volumetric expansion occurs during charging and discharging leading to capacity degradation
Solution Approach 1:
The silicon-based alloy is segmented into an inactive matrix phase and dispersed active silicon nanoparticle phases. This segmentation allows the inactive matrix to provide structural stability while the active silicon nanoparticles provide high capacity, resolving the contradiction between capacity improvement and capacity retention.
Solution Approach 2:
The invention uses a composite material structure consisting of an inactive matrix (comprising Ti2Ni phase and NiSi2 phase) with active silicon nanoparticles dispersed within. This composite structure combines the structural stability of the inactive matrix with the high capacity of active silicon, thereby improving both capacity and capacity retention.
2Quantity of substance
If Si and Sn are used to achieve high capacity, then discharge capacity is improved, but volumetric expansion during charging and discharging causes lifetime degradation
Solution Approach 1:
The inactive matrix acts as a pre-established cushioning structure that accommodates the volumetric expansion of active silicon nanoparticles during charging and discharging. This beforehand cushioning prevents structural degradation and maintains lifetime while preserving high discharge capacity.
Solution Approach 2:
The invention changes the physical and chemical parameters of the negative active material by creating a specific phase composition (inactive matrix with Ti2Ni and NiSi2 phases) and controlling particle size (10 nm to 200 nm for active silicon nanoparticles). These parameter changes enable the material to maintain structural integrity during volume changes, thereby extending lifetime while maintaining high discharge capacity.
3Quantity of substance
If active silicon content is increased to improve capacity, then discharge capacity increases, but volumetric expansion and side reactions increase leading to reduced lifetime
Solution Approach 1:
The inactive matrix serves as an intermediary between the active silicon nanoparticles and the external environment. It mediates the volumetric expansion by providing a flexible structural framework and reduces side reactions by limiting direct contact between active silicon and electrolyte, thereby enabling high discharge capacity with reduced harmful effects.
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 silicon-based alloy with a balanced composition and particle size distribution enhances discharge capacity and extends the battery's lifetime by buffering volumetric expansion and preventing side reactions, while maintaining a stable inactive matrix.
Implementation Method 1
enhances discharge capacity and extends the battery's lifetime by buffering volumetric expansion
Implementation Method 2
lithium ions are intercalated into and deintercalated from both a positive electrode and a negative electrode
Implementation Method 3
preventing side reactions, while maintaining a stable inactive matrix
Data Source
AI summary
A negative active material, a negative electrode, a lithium battery including the negative active material, and a method of manufacturing the negative active material, the negative electrode, and the lithium battery. The negative active material includes a silicon-based alloy including Si, Ti, Ni, and Fe components. The silicon-based alloy includes a Ti2Ni phase as an inactive phase and active silicon having a lower content than that of typical silicon-based alloys. The negative active material may improve discharge capacity and lifetime characteristics of lithium batteries.