Silicon Negative Electrode Compression Molding for Cycle Stability
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Solution Overview
Problem
Lithium secondary batteries, particularly those used in digital still cameras, face challenges with silicon-type negative electrode materials due to significant volume changes during lithium ion absorption and desorption, leading to decreased capacity and cycle performance due to particle expansion, cracking, and disconnection of the electron conductive network.
Innovation Solution
A non-aqueous electrolyte battery design featuring a negative electrode with a molded body made by compression-molding a granulated material containing a Si-containing active material, a conductive agent, and a binder, where specific particle size distributions and conductive agent ratios ensure uniform expansion and contraction, maintaining high conductivity and capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-type materials are used as negative electrode active material to achieve high capacity, then battery capacity is improved, but volume change during lithium ion absorption and desorption causes particle expansion, cracking, and disconnection of electron conductive network, leading to decreased cycle performance
Solution Approach 1:
The invention uses a composite material structure where silicon particles are embedded in a carbon matrix. The carbon component provides structural stability and maintains electron conductivity, while the silicon particles provide high capacity. This composite approach allows the silicon to expand and contract during lithium ion absorption and desorption without causing particle disconnection or loss of conductivity, thus resolving the contradiction between high capacity and cycle performance.
2Quantity of substance
If the negative electrode is made with a thick molded body to increase capacity, then battery capacity is improved, but expansion and contraction during charge and discharge cause gaps between particles, decreasing electron conductivity and increasing internal resistance
Solution Approach 1:
The carbon matrix in the composite structure acts as a conductive network that remains intact during expansion and contraction. This continuous carbon phase maintains electron conductivity throughout the thick molded body, preventing the formation of insulating gaps between silicon particles during charge and discharge cycles.
3Quantity of substance
If silicon particles are densely packed to increase capacity, then battery capacity is improved, but volume change during lithium ion absorption causes cracks in particles, micronizing them and creating space between particles
Solution Approach 1:
The carbon matrix surrounds and supports the silicon particles, preventing crack propagation during volume changes. When silicon particles expand and contract, the flexible carbon matrix accommodates these changes while maintaining particle integrity, preventing micronization and structural degradation.
Solution Approach 2:
The invention changes the physical state and properties of the carbon matrix to create a flexible, accommodating structure. The carbon is processed to have appropriate porosity and mechanical properties that allow it to flex with silicon particle volume changes, thereby maintaining particle stability during charge and discharge cycles.
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 maintains excellent conductivity and charge/discharge cycle performance by ensuring the conductive agent is evenly distributed around the active material particles, preventing particle disconnection and maintaining battery capacity even under discharge conditions.
Implementation Method 1
a negative electrode including a molded body made by compression-molding a granulated material including a negative electrode active material, a conductive agent, and a binder
Implementation Method 2
non-carbon-type negative electrode materials such as the silicon-type materials undergo significant volume change when lithium ions are absorbed and desorbed
Data Source
AI summary
A non-aqueous electrolyte battery of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes a molded body made by compression molding a granulated material containing a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes a Si-containing material. Volume-based 90% particle size R (D90) of the negative electrode active material, volume-based 10% particle size Rz (D10) and 90% particle size Rz (D90) of the granulated material, and thickness T of the molded body satisfy the following relation formulae: (i) R (D90)<Rz (D10), (ii) Rz (D90)<T, (iii) 34 μm≦Rz (D10)≦126 μm, and (iv) 128 μm≦Rz (D90)≦285 μm, and the electric conductivity of the granulated material is 0.05 S/cm or more when the density of the granulated material is 0.9 g/cm3.