Three-Layer Negative Electrode Sheet for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face a trade-off between high energy density and good fast-charging performance, as increasing the thickness of both positive and negative electrodes to meet energy density requirements deteriorates fast-charging capabilities.
Innovation Solution
A negative electrode sheet with a unique three-layer structure comprising a capacity providing layer, a conductive bonding layer, and a fast ion conductor layer, where the fast ion conductor layer is at the top to enhance lithium-ion transport and the capacity providing layer is at the bottom to maintain high energy density, with the bonding layer stabilizing the connection and providing volume buffering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the negative electrode is increased to meet energy density requirements, then the energy density is improved, but the fast-charging performance deteriorates
Solution Approach 1:
The negative electrode is divided into three distinct layers: a capacity providing layer (close to current collector) for high energy density, a fast ion conductor layer (close to separator) for rapid lithium-ion transport, and a conductive bonding layer for stabilization. This segmentation allows each layer to optimize for its specific function, resolving the contradiction between energy density and fast-charging performance.
Solution Approach 2:
Different regions of the negative electrode are assigned different functional qualities: the capacity providing layer uses high-capacity materials (silicon, tin, phosphorus) for energy storage, while the fast ion conductor layer uses materials with superior ionic conductivity for rapid charge acceptance. This local differentiation enables simultaneous optimization of both energy density and fast-charging capabilities.
2Speed
If the negative electrode sheet is made thin to improve fast-charging performance, then the fast-charging performance is improved, but the energy density decreases
Solution Approach 1:
By segmenting the electrode into functional layers, the invention achieves thin overall thickness for fast charging while concentrating high-capacity materials in the capacity providing layer to maintain energy density. The fast ion conductor layer thickness is optimized for rapid ion transport, while the capacity providing layer compensates for energy storage.
3Quantity of substance
If high-capacity materials are used in the negative electrode to increase energy density, then the energy density is improved, but the volume expansion during charging increases
Solution Approach 1:
The conductive bonding layer acts as an intermediary between the capacity providing layer and fast ion conductor layer, providing mechanical support and accommodating volume expansion of high-capacity materials during charging cycles. This intermediary layer prevents direct transmission of expansion stresses to other components.
Solution Approach 2:
The conductive bonding layer is designed with cushioning properties to anticipate and accommodate the volume expansion of high-capacity materials during lithium insertion. This pre-designed cushioning capacity prevents structural damage before expansion occurs, enabling use of high-capacity materials without compromising electrode integrity.
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 achieves high capacity utilization, high energy density, short charging time, and good cycling performance by optimizing lithium-ion transport and accommodating volume changes, thereby improving fast-charging performance and cycling stability.
Implementation Method 1
The fast ion conductor layer includes a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent
Implementation Method 2
The conductive bonding layer is arranged between the capacity providing layer and the fast ion conductor layer to stabilize connection of the foregoing two layers, and provide a buffering space for volume expansion of the negative electrode during charging
Data Source
AI summary
A negative electrode sheet includes a negative electrode current collector as well as a capacity providing layer, a conductive bonding layer, and a fast ion conductor layer which are sequentially stacked on at least one side surface of the negative electrode current collector, where the capacity providing layer comprises a first negative electrode active material, a first binder, and a first conductive agent, the fast ion conductor layer comprises a carbon active material, a lithium superionic conductor, a second binder, and a second conductive agent, and the specific capacity of the first negative electrode active material is greater than that of the carbon active material.