Mg-Coated Silicon-Carbon Anode Material for Longer Battery Cycle Life
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Solution Overview
Problem
Existing rechargeable lithium batteries face challenges in achieving improved charge and discharge characteristics and cycle-life characteristics, particularly due to the expansion of silicon-based materials in the negative active material, which affects energy density and efficiency.
Innovation Solution
A negative active material comprising a crystalline carbon core with a magnesium (Mg)-included coating layer containing MgO and MgxSiOy (1≤x≤2 and 3≤y≤4) is prepared by adding crystalline carbon to an acidic solvent, followed by a sol-gel reaction with a hydrogen silsesquioxane precursor, heat-treatment, and doping with a Mg source material to form a stable coating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silicon-based material is used in negative active material to increase capacity, then energy density is improved, but expansion occurs leading to degraded cycle-life characteristics
Solution Approach 1:
The patent employs a multi-layer nested coating structure where an inner amorphous carbon layer directly coats the silicon-based material core, providing initial stabilization. An outer crystalline carbon layer is then formed on top of the amorphous carbon layer, creating a nested protective structure. This nested doll approach allows the silicon-based material to expand and contract during cycling while maintaining structural integrity and preventing direct exposure to the electrolyte, thus resolving the contradiction between high energy density and cycle-life characteristics.
Solution Approach 2:
The patent utilizes composite materials by combining silicon-based material with carbon materials in a layered structure. The composite consists of a silicon-based core (providing high capacity) surrounded by amorphous carbon and crystalline carbon layers (providing structural stability). This composite material approach allows the system to simultaneously achieve the high energy density of silicon while maintaining the cycle-life characteristics through the stabilizing carbon composite structure.
2Reliability
If coating layer is added to stabilize silicon-based material, then cycle-life characteristics are improved, but initial efficiency decreases due to increased impedance
Solution Approach 1:
The patent applies local quality by creating different types of carbon coatings with distinct properties at different locations. The inner amorphous carbon layer provides flexible accommodation for silicon expansion, while the outer crystalline carbon layer provides structural stability and conductivity. This localized differentiation of coating properties allows the system to achieve both improved cycle-life characteristics and maintained initial efficiency by optimizing each layer's function rather than using a uniform coating.
Solution Approach 2:
The patent employs parameter changes by controlling the carbonization process to create a gradient structure from amorphous to crystalline carbon. By adjusting heat treatment parameters (temperature, time, atmosphere), the patent transforms the carbon structure to achieve optimal balance between stability and conductivity. This parameter optimization allows the coating to provide protection while minimizing impedance increase, thus resolving the contradiction between cycle-life improvement and initial efficiency maintenance.
3Stability of the object's composition
If crystalline carbon is used as negative active material, then structural stability is improved, but capacity is limited compared to silicon-based materials
Solution Approach 1:
The patent uses the nested doll principle by placing low-capacity but stable crystalline carbon as the outer layer and high-capacity silicon-based material as the inner core. This nested structure allows the system to benefit from both the high capacity of silicon (inner layer) and the structural stability of crystalline carbon (outer layer), effectively resolving the contradiction between structural stability and capacity.
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 solution enhances energy density, initial efficiency, and cycle-life characteristics by stabilizing the silicon-based material, preventing expansion, and improving electrical conductivity and mechanical strength.
Implementation Method 1
adding a hydrogen silsesquioxane precursor to the mixed liquid to prepare a mixture; primarily heat-treating the mixture to prepare a primarily heat-treated product
Implementation Method 2
secondarily heat-treating the mixed product
Implementation Method 3
mixing the primarily heat-treated product with a Mg source material to prepare a mixed product; and secondarily heat-treating the mixed product
Data Source
AI summary
A negative active material, a method of preparing the negative active material, and a rechargeable lithium battery including the negative active material are disclosed. The negative active material may include a crystalline carbon core and a magnesium (Mg)-included coating layer on a surface of the core, wherein the Mg-included coating layer may include MgO and MgxSiOy (1≤x≤2 and 3≤y≤4).