Dual-Layer Negative Electrode Sheet for Fast-Charge Capacity
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Solution Overview
Problem
Lithium-ion batteries with functional layers formed by mixing graphite and silicon particles exhibit reduced fast charging ability, affecting their charging and discharging performance under high current conditions.
Innovation Solution
A negative electrode sheet with a dual-layer structure, where the first layer near the current collector contains silicon and hard carbon particles, and the second layer further away contains graphite particles, allowing lithium ions to be embedded gradually, reducing concentration accumulation and improving dynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite particles and silicon particles are mixed to form a functional layer, then the capacity of lithium-ion battery is improved, but the fast charging ability is reduced
Solution Approach 1:
The negative electrode sheet is divided into two distinct layers: a first negative electrode film layer containing silicon particles and hard carbon particles, and a second negative electrode film layer containing graphite particles. This segmentation allows different materials to be positioned at different locations, enabling the battery to achieve both high capacity (from silicon) and fast charging ability (from graphite's superior ion transport properties).
Solution Approach 2:
Different regions of the negative electrode are assigned different material compositions tailored to their specific functions. The first layer near the current collector uses silicon particles for high capacity storage, while the second layer uses graphite particles for fast ion embedding and discharge. This local quality differentiation optimizes both capacity and fast charging performance simultaneously.
2Quantity of substance
If silicon particles are used in the functional layer, then the energy density is improved, but lithium-ion precipitation occurs during fast charging
Solution Approach 1:
Hard carbon particles are introduced as an intermediary material between silicon particles and the electrolyte. These hard carbon particles have better lithium-ion embedding and discharge performance than silicon, acting as a buffer that prevents direct lithium-ion precipitation on silicon particles during fast charging, thereby maintaining both high energy density and reliability.
Solution Approach 2:
The hard carbon particles are pre-positioned around the silicon particles in the first negative electrode film layer before battery operation. This preliminary arrangement ensures that lithium-ions are first embedded into the hard carbon particles, which have sufficient time and capacity to accommodate the ions before they reach the silicon particles, preventing precipitation in advance.
3Device complexity
If a single-layer functional structure is used, then the device complexity is reduced, but the charging speed is limited
Solution Approach 1:
The negative electrode structure transitions from a single-layer configuration to a two-layer configuration, adding a dimensional aspect to the electrode design. This dimensional change allows different materials to be arranged in layers, creating a gradient structure that optimizes ion transport pathways and enhances charging speed without excessive complexity.
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 charging speed and endurance of lithium-ion batteries by managing lithium ion distribution and reducing precipitation, thereby addressing the reduction in fast charging capacity.
Implementation Method 1
when the lithium-ions move to the negative electrode sheet, part of the lithium-ions are first embedded into the graphite particles in the second negative electrode film layer, and the remaining lithium-ions are embedded into the first negative electrode film layer
Data Source
AI summary
A negative electrode sheet, including a negative current collector, where a first negative electrode film layer is attached to a surface of the negative current collector, and an active substance of the first negative electrode film layer includes silicon particles and hard carbon particles; a second negative electrode film layer is attached to a surface of the first negative electrode film layer, and an active substance of the second negative electrode film layer includes graphite particles, such that when lithium-ions move to the negative electrode sheet, part of lithium-ions are first embedded into the second negative electrode film layer, and the remaining lithium-ions are embedded into the first negative electrode film layer.