Silicon Negative Electrode Gradient Distribution for Battery Cycle Life
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries using silicon as a negative electrode material face issues with volume change during lithium insertion and desorption, leading to internal short circuits and reduced cycle life due to the high energy density requirements and safety concerns.
Innovation Solution
A negative electrode composition comprising silicon, silicon oxide, and a carbonaceous material with a specific distribution of silicon concentrations in the electrode mixture layer, where silicon concentrations are higher at the surfaces and lower at the center, combined with a carbonaceous material phase for improved conductivity and stress reduction, is used to mitigate volume changes and prevent internal short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to increase energy density, then the negative electrode capacity per mass increases about 10 times compared to graphitic carbon, but the volume of the negative electrode largely changes during charge and discharge cycles causing internal short circuits
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of silicon concentration within the negative electrode active material particles. The surface region has a different silicon concentration (higher or lower depending on the embodiment) compared to the interior region, which allows the surface to accommodate volume changes during lithium insertion/extraction while maintaining structural integrity and preventing internal short circuits.
Solution Approach 2:
The patent uses composite materials by combining silicon with other elements or compounds to form alloys or compounds such as silicon oxide, silicon nitride, or silicon-based composite materials. This composite structure enables the negative electrode to achieve high capacity while mitigating the harmful volume expansion effects through the synergistic properties of the constituent materials.
2Quantity of substance
If silicon absorbs lithium until the atomic ratio Li/Si reaches 4.4 to maximize capacity, then the negative electrode capacity per mass becomes about 10 times that of graphitic carbon, but the volume change associated with lithium insertion and desorption causes the negative electrode to go beyond usual charge and discharge ranges
Solution Approach 1:
The patent implements local quality by establishing different silicon concentrations in different regions of the active material particles. The surface region has a modified silicon concentration that provides buffer capacity for volume changes, allowing the interior region to maintain optimal lithium storage capacity while the surface accommodates the mechanical stress of expansion and contraction during full charge-discharge cycles.
Solution Approach 2:
The patent applies beforehand cushioning by pre-structuring the negative electrode active material with a specific silicon concentration gradient before lithium insertion begins. The surface region is designed with appropriate silicon concentration to act as a cushion that absorbs the mechanical stress of volume changes, preventing structural collapse and maintaining stable charge-discharge ranges even when lithium absorption reaches the Li/Si = 4.4 ratio.
3Use of energy by moving object
If the volume of the negative electrode changes during charge and discharge cycles, then the battery can achieve high energy density, but an internal short circuit occurs and the resistance of the electrode is increased causing excessive electrification and voltage drop
Solution Approach 1:
The patent applies local quality by creating a non-uniform silicon concentration distribution where the surface region has a different concentration than the interior. This gradient structure allows the surface to accommodate volume changes and maintain electrical contact, preventing internal short circuits and excessive resistance increases while enabling the interior to provide high energy density through optimal lithium storage.
Solution Approach 2:
The patent uses composite materials such as silicon-based alloys or compounds that combine the high capacity of silicon with materials that provide structural stability and electrical conductivity. This composite approach maintains low electrode resistance and stable voltage characteristics during volume changes while achieving high energy density.
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 configuration enhances the large current discharge characteristics and cycle life of the battery while preventing internal short circuits, maintaining battery safety and performance.
Implementation Method 1
silicon can absorb lithium until the atomic ratio Li/Si of lithium atoms to silicon atoms reaches 4.4
Implementation Method 2
a carbonaceous material phase for improved conductivity
Data Source
AI summary
A negative electrode for a nonaqueous electrolyte secondary battery of the embodiment includes a current collector; and an electrode mixture layer that is formed on the current collector and contains a first particle, a second particle and a binder. The first particle is comprised of silicon, a silicon oxide and a carbonaceous material. The second particle has electron conductivity and an oxygen content of 1% or lower. The electrode mixture layer is characterized in that silicon concentrations in the vicinity of the surface having contact with the current collector and the vicinity of the opposite surface to the surface having contact with the current collector are higher than a silicon concentration at the central part in the thickness direction.