Battery Electrode Modulus Gradient for High-Rate Cycling Stability
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Solution Overview
Problem
Electrical storage devices experience capacity reduction and increased resistance during charge and discharge cycles, particularly during high-rate operations, due to expansion and contraction of the electrode body pressing electrolytic solution out, leading to increased battery resistance.
Innovation Solution
An electrical storage device with a negative electrode having a higher compression modulus in its surface layer and a lower compression modulus near the current collector, a separator with a lower compression modulus than the first layer, and an elastic body with a lower compression modulus than the separator, to absorb and manage the expansion and contraction, thereby maintaining electrolyte retention and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the electrode body expands and contracts during charge and discharge, then charge carriers are occluded and released into and from the active materials, but the electrolytic solution is pressed out of the electrode body leading to increased battery resistance
Solution Approach 1:
The negative-electrode active material layer is designed with different compression moduli at different depths: the first layer (near current collector) has compression modulus of 0.1-10 MPa, while the second layer (surface layer) has 10-100 MPa. This gradient structure allows the deeper region to accommodate expansion/contraction while the surface layer maintains electrolyte retention, resolving the contradiction between charge transfer capability and resistance control.
Solution Approach 2:
The invention changes the physical parameter (compression modulus) of the negative-electrode active material layer by controlling the graphitization degree. The first layer has lower graphitization (lower compression modulus) to allow expansion, while the second layer has higher graphitization (higher compression modulus) to retain electrolyte, thus managing the contradiction through parameter variation.
2Reliability
If the negative electrode has a higher compression modulus than the separator, then the retainability of electrolytic solution is improved and battery resistance increase is suppressed, but the electrode body expansion and contraction is constrained
Solution Approach 1:
The negative electrode is structured with two layers having different compression moduli. The first layer (0.1-10 MPa) is softer to allow expansion, while the second layer (10-100 MPa) is harder to retain electrolyte. This local differentiation resolves the contradiction between maintaining electrolyte and allowing expansion.
Solution Approach 2:
The negative-electrode active material layer is segmented into two distinct layers with different mechanical properties. The first layer handles expansion/contraction, while the second layer handles electrolyte retention, dividing the conflicting functions into separate zones.
3Productivity
If electrical storage devices undergo repeated charge and discharge cycles, then capacity is utilized, but capacity decreases over time reducing device life
Solution Approach 1:
The two-layer negative electrode structure with different compression moduli allows the device to undergo repeated cycling while maintaining capacity. The first layer accommodates volume changes during cycling, while the second layer maintains electrolyte contact, enabling both high cycling productivity and capacity retention.
Solution Approach 2:
The negative electrode uses a composite structure of two layers with different graphitization degrees and mechanical properties. This composite design enables the electrode to withstand repeated cycling while maintaining both structural integrity and electrolyte retention, improving capacity retention over time.
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 effectively suppresses the increase in resistance during high-rate charge and discharge and maintains capacity by absorbing the stress of expansion and contraction, ensuring better electrolyte retention and reduced capacity loss over charge and discharge cycles.
Implementation Method 1
the negative-electrode active material layer includes a first layer formed on the negative-electrode current collector, and a second layer that is formed on the first layer and has a higher compression modulus than the first layer
Implementation Method 2
the elastic body has a lower compression modulus than the separator... to absorb and manage the expansion and contraction
Implementation Method 3
the separator has a lower compression modulus than the first layer
Implementation Method 4
an elastic body configured to receive a load from the electrode body in the stacking direction of the electrode body... having a lower compression modulus than the separator
Data Source
AI summary
An advantage of the present invention is to suppress an increase in resistance during high-rate charge and discharge and a reduction in capacity during a charge and discharge cycle. An electrical storage module of the present embodiment includes: an electrical storage device, and an elastic body that is placed with the electrical storage device and receives a load from the electrical storage device in a placement direction. The electrical storage device includes a positive electrode, a negative electrode, and a separator. The negative electrode includes a negative-electrode active material layer. The negative-electrode active material layer includes a first layer formed on the negative-electrode current collector, and a second layer that is formed on the first layer and has a higher compression modulus than the first layer. The separator has a lower compression modulus than the first layer, and the elastic body has a lower compression modulus than the separator.