Silicon Alloy Negative Electrode for High-Capacity Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries for vehicle applications face challenges in achieving high cycle durability due to the large volume expansion and contraction of silicon-based negative electrode materials during charge and discharge, which compromises their capacity and lifespan.
Innovation Solution
A silicon-containing alloy with a silicide phase of a transition metal dispersed in an amorphous or low crystalline silicon parent phase, where the ratio of diffraction peak intensity of the silicide to the (111) plane of Si is controlled within specific ranges to suppress phase transitions and maintain structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based negative electrode material is used to achieve high capacity, then the energy density is improved, but the volume expansion and contraction during charge and discharge causes great volume change (about 4 times), leading to decreased cycle lifespan
Solution Approach 1:
The invention changes the crystalline state parameter of silicon to an amorphous state, which suppresses the phase transition that causes great volume change during charge and discharge. This parameter change maintains high capacity while reducing volume expansion and contraction, thereby improving cycle lifespan
Solution Approach 2:
The invention uses a composite material structure where amorphous silicon is combined with a specific amount of crystalline silicon or silicon-containing compounds. This composite approach allows the material to maintain high capacity from crystalline regions while the amorphous regions suppress harmful phase transitions, resolving the contradiction between capacity and cycle lifespan
2Quantity of substance
If a silicon-based negative electrode material is used to achieve high capacity, then the energy density is improved, but the capacity and cycle durability have a trade-off relationship, making it difficult to improve cycle durability while having high capacity
Solution Approach 1:
The invention changes the structural parameter of silicon from crystalline to amorphous state, which fundamentally alters the charge-discharge mechanism to prevent capacity fade over cycles. This allows simultaneous achievement of high capacity and improved cycle durability
Solution Approach 2:
The invention creates local quality differences by having amorphous silicon regions combined with small amounts of crystalline silicon or silicon-containing compounds. The amorphous regions provide stable cycle durability while the crystalline regions contribute to high capacity, achieving both goals simultaneously
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
This approach enhances the cycle durability and capacity of lithium ion secondary batteries by minimizing volume changes during charge and discharge, leading to improved performance and lifespan.
Implementation Method 1
a silicon-containing alloy having a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a parent phase containing amorphous or low crystalline silicon as a main component... the ratio value (B/A) of a diffraction peak intensity B of silicide of a transition metal... to a diffraction peak intensity A of a (111) plane of Si... is 0.41 or more... capable of suppressing a phase transition when Si is alloyed with Li
Implementation Method 2
a battery using a material to be alloyed with Li in the negative electrode is expected as a negative electrode material in a vehicle application... Si+3.75Li++e−Li3.75Si
Data Source
AI summary
A negative electrode active material for electric device is used which includes a silicon-containing alloy having a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a parent phase containing amorphous or low crystalline silicon as a main component and a predetermined composition and in which a ratio value (B/A) of a diffraction peak intensity B of a silicide of a transition metal in a range of 2θ=37 to 45° to a diffraction peak intensity A of a (111) plane of Si in a range of 2θ=24 to 33° is 0.41 or more in an X-ray diffraction measurement of the silicon-containing alloy using a CuKα1 ray.