Core-Shell Silicon Anode Material for Higher Coulombic Efficiency
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Solution Overview
Problem
Lithium-ion secondary batteries face limitations in energy density due to low first coulombic efficiency and reversible specific capacity, primarily attributed to the limited gram capacity of graphite-based negative electrode active materials, which restricts the utilization of silicon components and results in insufficient energy density improvement.
Innovation Solution
A negative electrode active material with a core-shell structure is developed, comprising an inner core of silicon and lithium silicate, an interlayer of silicon or silicon-lithium silicate, and an outer shell of amorphous carbon, enhancing silicon content and suppressing side reactions with the electrolyte, thereby improving coulombic efficiency and specific capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If graphite-based negative electrode active materials are used, then the battery structure is simple and manufacturing is easy, but the energy density and reversible specific capacity are limited
Solution Approach 1:
The patent employs a composite negative electrode active material comprising graphite particles coated with a silicon-based coating layer containing Li-Si-O amorphous phase. This composite structure combines the structural stability and ease of manufacture of graphite with the high capacity of silicon, achieving both manufacturing simplicity and improved energy density
Solution Approach 2:
The patent modifies the chemical composition and phase structure of the coating layer by controlling the Li/Si atomic ratio and creating an amorphous Li-Si-O phase. This parameter change enables the coating layer to simultaneously provide structural stability and high lithium ion capacity, resolving the contradiction between manufacturing ease and energy density
2Quantity of substance
If silicon content in the negative electrode is increased to improve energy density, then the reversible specific capacity increases, but side reactions with electrolyte increase and coulombic efficiency decreases
Solution Approach 1:
The patent introduces a graphite-based negative electrode active material as an intermediary substrate that provides structural stability and acts as a barrier between the silicon-based coating layer and the electrolyte. This intermediary structure reduces direct contact between silicon and electrolyte, minimizing side reactions while maintaining high reversible specific capacity
Solution Approach 2:
The patent creates a sacrificial amorphous phase in the coating layer that preferentially reacts with electrolyte during initial cycles, forming a stable solid electrolyte interface (SEI) layer. This disposable reactive phase protects the bulk silicon from continuous side reactions, improving coulombic efficiency while maintaining high capacity
3Quantity of substance
If the first coulombic efficiency is improved by reducing side reactions, then the energy density improvement is limited, but if energy density is prioritized, then coulombic efficiency decreases
Solution Approach 1:
The patent creates different functional zones within the negative electrode: the inner graphite core provides structural stability and low side reactions, while the outer silicon-based coating layer provides high capacity. This local quality differentiation allows the battery to achieve high energy density from the silicon layer while maintaining good coulombic efficiency through the graphite core's stability
Solution Approach 2:
The patent employs a nested structure where the silicon-based coating layer is coated onto the graphite negative electrode active material particles. The graphite particles are nested within the coating layer, creating a core-shell structure that combines the advantages of both materials: graphite's stability and silicon's high capacity, achieving both high energy density and acceptable coulombic efficiency
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 novel core-shell structure significantly increases the energy density of secondary batteries by optimizing silicon content and reducing side reactions, leading to enhanced coulombic efficiency and specific capacity utilization.
Implementation Method 1
subjecting the inner core precursor to an alkaline solution etching treatment, so that a recessed structure is formed on the surface of the inner core precursor
Implementation Method 2
placing inner core in a vapor deposition system, and introducing a first mixed gas to carry out a first reaction, so that the surface of the inner core is cladded with an interlayer
Implementation Method 3
placing the first intermediate in a vapor deposition system, and introducing a second mixed gas to carry out a second reaction, so that an outer shell layer is formed on the interlayer
Implementation Method 4
subjecting the second intermediate to a solid pre-lithiation reaction with a pre-lithiation agent to form a pre-lithiated body
Data Source
AI summary
A negative electrode active material and a preparation method, a secondary battery, a battery module, a battery pack and an electrical apparatus are provided. The negative electrode active material comprises an inner core, an interlayer and an outer shell layer, wherein the interlayer is cladded on the surface of the inner core, and the outer shell layer is cladded on the surface of the interlayer; the inner core comprises silicon, an oxide of silicon and lithium silicate; the interlayer comprises silicon, or silicon and lithium silicate; and the outer shell layer comprises amorphous carbon. An inner core comprising silicon, an oxide of silicon and lithium silicate is used as a nucleus, and an interlayer containing silicon as well as an outer shell layer comprising amorphous carbon are cladded outwards in sequence to form a uniformly cladded and structurally stable negative electrode active material with a core-shell structure.