Conductive Sheet for Lithium-Ion Battery Electrodes
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Solution Overview
Problem
Existing storage devices, particularly lithium ion secondary batteries and electric double layer capacitors, face challenges with negative electrodes that experience volumetric expansion, leading to conductivity reduction and structural issues, such as particulate active materials collapsing and separating from the electrode collector layer, which complicates the preparation and reduces productivity.
Innovation Solution
A conductive sheet comprising a laminated structure of a sheet (A) with specific fiber diameters and apparent specific gravity, and a conductive ultrafine fiber sheet (B) with even smaller fiber diameters, forming a three-dimensional network that secures conductive paths and relaxes stress from active materials, allowing for improved charge collection and reduced internal resistance without the need for binders or auxiliary conducting agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sintering process is used to prepare negative electrode with copper or copper alloy collector, then conductivity is improved, but Cu-Si compound formation occurs that is electrochemically non-reactive with lithium, resulting in reduction in capacity
Solution Approach 1:
The invention extracts copper from the electrode collector material and replaces it with aluminum, which does not form electrochemically non-reactive compounds with silicon. This eliminates the harmful Cu-Si compound formation while maintaining the collector's conductivity function.
Solution Approach 2:
The invention changes the material parameter of the electrode collector from copper or copper alloy to aluminum or aluminum alloy. This parameter change prevents the formation of non-reactive compounds with lithium while maintaining or improving conductivity and avoiding high-temperature sintering requirements.
2Reliability
If sintering is performed at high temperature to prepare negative electrode, then conductivity is improved, but copper used for electrode collector element comes to melt or harden, losing flexibility required for electrode collector element
Solution Approach 1:
The invention changes the collector material to aluminum, which has a lower melting point than copper but can be processed at temperatures below its melting point to achieve good conductivity without sintering. This avoids the hardening and flexibility loss issues associated with high-temperature copper sintering.
Solution Approach 2:
The invention replaces the mechanical sintering process with a coating process where conductive material is applied to the aluminum collector surface. This eliminates the need for high-temperature sintering that causes copper to harden and lose flexibility.
3Stability of the object's composition
If photoresist technique and electroplating technique are employed to form anode active material layer with selective concave-convex pattern, then volumetric expansion is accommodated, but preparation of photoresist mask is needed that complicates preparation and limits productivity
Solution Approach 1:
The invention extracts and eliminates the photoresist mask preparation step from the manufacturing process. Instead of using complex patterning techniques, it employs a simple coating method where conductive material and binder are applied directly to the aluminum collector, achieving both expansion accommodation and high productivity.
Solution Approach 2:
The invention uses a porous or fibrous conductive material structure that can accommodate volumetric expansion of the active material without requiring complex concave-convex patterning. The porous structure provides space for expansion while maintaining electrical conductivity and mechanical integrity.
4Manufacturing precision
If paste prepared by kneading binder, active material and conductive agent together is coated on electrode collector foil, then electrode is formed, but sophisticated selection of binder and high level technique are required to increase uniformity and density, encountering difficulties
Solution Approach 1:
The invention uses a composite material system where conductive material particles are dispersed in a binder that is then coated on the aluminum collector. This composite approach simplifies the formulation requirements compared to traditional paste kneading, achieving good uniformity and density with less sophisticated binder selection and simpler processing.
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 conductive sheet enhances discharge capacity, cycle characteristics, and charge collecting properties by preventing active material collapse and loss, while simplifying the manufacturing process and improving the electrode's ability to handle high volumetric expansion, resulting in higher performance storage devices.
Implementation Method 1
the conductive sheet has a three-dimensional network of entangled conductive fibers in both sheets (A) and (B) and can achieve to produce conductive paths everywhere in the whole electrode layer
Implementation Method 2
the conductive sheet can make a contribution to stress relaxation of active material having high volumetric expansion
Data Source
AI summary
The present invention provides a conductive sheet having a surface resistance of 10 Ω/sq or lower on both surfaces, the conductive sheet comprising a sheet (A) and a sheet (B) laminated to the sheet (A), the sheet (A) having an apparent specific gravity of 0.05 g/cm3 to 0.50 g/cm3 and being formed from fibers having a diameter within the range between 3 and 20 µm, and the sheet (B) being formed from fibers having a diameter of 3 µm or smaller. The sheet (A) may be a fibrous material comprises an organic polymer fiber as its main component.