Silicon Negative Electrode with Silicon Oxide Coating for Cycle Stability
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Solution Overview
Problem
Lithium-ion secondary batteries with silicon electrodes face challenges such as expansion and contraction issues leading to conductive path loss, deformation, and reduced capacity due to the high reactivity of silicon with carrier ions, which accelerates electrolyte decomposition and reduces the battery's lifespan, especially at high temperatures.
Innovation Solution
A negative electrode active material with a layered structure comprising a first region of high-capacity elements like silicon and a second region with lower reactivity, such as silicon oxide, is used to mitigate expansion and contraction, maintaining contact with the current collector and reducing electrolyte decomposition, thereby enhancing cycle stability and charge/discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative electrode active material to increase capacity, then theoretical capacity increases dramatically, but expansion and contraction cause conductive path loss and reduced cycle life
Solution Approach 1:
The silicon layer is divided into multiple fine particles (average particle size 1 μm to 100 μm) and dispersed on an uneven current collector surface. This segmentation reduces expansion stress concentration and prevents large-scale conductive path loss during charge-discharge cycles.
Solution Approach 2:
A protective coating layer is formed over the silicon particles, creating a nested structure where the coating protects the silicon core from excessive expansion and maintains conductive pathways. This nested configuration allows silicon to achieve high capacity while the coating preserves cycle stability.
2Quantity of substance
If silicon expands and contracts with carrier ion reception and release, then capacity increases, but contact states between active material and conductive additive deteriorate
Solution Approach 1:
A protective coating is applied beforehand to cushion the expansion and contraction of silicon particles during charge-discharge cycles. This pre-applied protective layer maintains contact between silicon, conductive additives, and current collector even during volume changes.
Solution Approach 2:
A flexible protective coating layer is formed over silicon particles, allowing the coating to accommodate expansion and contraction while maintaining electrical conductivity and mechanical contact. This thin film structure preserves conductive pathways during capacity cycling.
3Power
If high temperature operation is performed to increase power output, then charge and discharge rate increases, but electrolyte decomposition accelerates
Solution Approach 1:
A protective coating layer acts as an intermediary between silicon and electrolyte, reducing direct contact and harmful reactions at high temperatures. This intermediate layer allows high-rate charge-discharge while suppressing electrolyte decomposition through chemical barrier properties.
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 structure improves the cycle characteristics and charge/discharge efficiency of lithium-ion batteries by reducing stress and reactivity, leading to higher capacitance and extended operating temperature ranges, while maintaining the battery's integrity and capacity over cycles.
Implementation Method 1
a second region with lower reactivity, such as silicon oxide, is used to mitigate expansion and contraction
Implementation Method 2
The proposed structure improves the cycle characteristics and charge/discharge efficiency of lithium-ion batteries by reducing stress and reactivity
Implementation Method 3
when the material that is alloyed and dealloyed with lithium (e.g., silicon) greatly expands and contracts with reception and release of carrier ions in charge and discharge cycles
Data Source
AI summary
A power storage device with high capacity is provided. Alternatively, a power storage device with excellent cycle characteristics is provided. Alternatively, a power storage device with high charge and discharge efficiency is provided. Alternatively, a power storage device with a long lifetime is provided. A negative electrode active material includes a first region and a second region. The first region includes at least one element selected from Si, Mg, Ca, Ga, Al, Ge, Sn, Pb, Sb, Bi, Ag, Zn, Cd, As, Hg, and In. The second region includes oxygen and the same element as the one included in the first region. The crystallite size of the element included in the first region is larger than or equal to 1 nm and smaller than or equal to 10 nm.