Porous Silicon-Carbon Anode Layer for Fast-Charging Capacity
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Solution Overview
Problem
Conventional electrochemical apparatuses with graphite negative electrodes have limited capacity and struggle to meet rapid charge and discharge demands due to graphite's low theoretical gram capacity and inferior electronic/ionic conductivity compared to silicon.
Innovation Solution
The electrochemical apparatus incorporates an electrode sheet with a current collector and an active material layer containing a high-capacity first active material (such as silicon) and a second active material (such as carbon), along with a first pore structure that enhances lithium ion transmission and reduces impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon material is used as negative electrode active material, then gram capacity is improved, but electronic/ionic conductivity deteriorates
Solution Approach 1:
The patent uses composite active material layer containing both silicon-based material (for high capacity) and conductive material (for improved conductivity). This composite structure allows the electrode to achieve both high gram capacity and acceptable electronic/ionic conductivity by combining the advantages of different materials.
Solution Approach 2:
The patent introduces porous structure in the active material layer to improve electrolyte penetration and ion transport. The porous structure increases the surface area for electrochemical reactions and facilitates faster lithium ion diffusion, thereby improving ionic conductivity while maintaining high capacity from silicon-based materials.
2Quantity of substance
If silicon material is used as negative electrode active material, then gram capacity is improved, but charge and discharge rate deteriorates
Solution Approach 1:
The porous structure in the active material layer significantly enhances charge and discharge rates by providing multiple pathways for lithium ion diffusion. The increased surface area and improved electrolyte access allow faster electrochemical reactions, enabling the high-capacity silicon-based material to deliver its capacity at higher rates.
Solution Approach 2:
The active material layer is segmented into a composite structure with conductive material distributed throughout, creating multiple localized conductive networks. This segmentation reduces electron transport distances and facilitates faster charge transfer, improving overall charge and discharge kinetics.
3Quantity of substance
If mass percentage of first active material is increased, then capacity is improved, but kinetic performance deteriorates
Solution Approach 1:
The patent optimizes the mass percentage of first active material within a specific range (10-80%) rather than using maximum possible content. This parameter optimization balances capacity and kinetic performance, ensuring sufficient conductive material remains to maintain good electron transport while maximizing the capacity-contributing active material.
Solution Approach 2:
The composite active material layer maintains a controlled ratio between high-capacity first active material and conductive second active material. This composite approach ensures that even as first active material content increases for higher capacity, enough conductive material remains to preserve acceptable kinetic performance.
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 increases the capacity and charge/discharge speed of the electrochemical apparatus by optimizing the mass percentage and porosity of the active material layer, reducing impedance, and improving kinetic performance to meet rapid charge and discharge demands.
Implementation Method 1
The first pore structure can be fully infiltrated and filled by an electrolyte, and becomes a new lithium ion liquid phase transmission channel, replacing the fixed channel with a low diffusion coefficient. The lithium ions deeply intercalate into the electrode sheet through the newly constructed first pore structure.
Data Source
AI summary
An active material layer is provided with at least one first pore structure, and the active material layer satisfies the following conditions: (a) 0≤M/d≤0.5, where M is a mass percentage of the first active material in the active material layer, and d is a ratio of a depth of the first pore structure to a thickness of the active material layer; and (b) −1%≤0.2M−S≤3%, where S is a porosity of the active material layer. Adding the first active material with a larger gram capacity can increase the capacity of the electrochemical apparatus.