Lithium Ion Battery Electrode Thickness Optimization
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Solution Overview
Problem
Lithium ion batteries face degradation in properties at large current due to increased diffusion distance of lithium ions in thick electrode layers, which limits their application in high-output power devices like electric automobiles.
Innovation Solution
A lithium ion battery design with specific thickness and density ranges for both positive and negative electrode mixture layers, along with the use of lithium composite oxides and graphite as active materials, and the addition of carbon fiber to enhance diffusivity, ensuring that the diffusion of lithium ions is not rate-determining in either electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the electrode mixture layers is increased to raise energy density, then the energy density is improved, but the properties at large current are degraded due to increased lithium ion diffusion distance
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the positive electrode mixture layer (60-85 μm) and negative electrode mixture layer (40-75 μm) within specific ranges. This optimization balances the diffusion distance for lithium ions with the energy density requirements, ensuring that the layers are thick enough to provide high energy density but thin enough to maintain acceptable ion diffusion speed for large current properties.
2Quantity of substance
If the thickness of the mixture layers is increased to improve energy density, then the energy density is improved, but the output properties are degraded
Solution Approach 1:
The patent optimizes the thickness parameters of the electrode mixture layers to fall within specific ranges (positive: 60-85 μm, negative: 40-75 μm). This parameter optimization ensures that the electrode layers are sufficiently thick to achieve high energy density while remaining thin enough to maintain good output properties by limiting lithium ion diffusion distance.
Solution Approach 2:
The patent uses composite materials including lithium composite oxide as the positive electrode active material and graphite as the negative electrode active material. These composite material selections contribute to achieving both high energy density and satisfactory output properties by providing favorable electrochemical characteristics and ion transport properties.
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 battery maintains satisfactory properties at large current and achieves high energy density, suitable for applications requiring high output power such as electric automobiles, with an energy density of 80 Wh/kg or more.
Implementation Method 1
the diffusion process of lithium ion is rate determining due to the increased diffusion distance of lithium ion in the electrode
Data Source
AI summary
An object of the present invention is to provide a lithium ion battery which is excellent in properties at large current and can be applied to applications requiring high output power even when the mixture layers are made thick. The present invention provides a lithium ion battery including a positive electrode including a positive electrode mixture layer formed on a current collector, a negative electrode including a negative electrode mixture layer formed on a current collector and an electrolyte, the positive electrode and the negative electrode being disposed through the intermediary of a separator, wherein the positive electrode includes as a positive electrode active material a lithium composite oxide represented by LiNiaMnbCOcMdO2 (in the formula, M is at least one selected from the group consisting of Fe, V, Ti, Cu, Al, Sn, Zn, Mg, B and W, a+b+c+d=1, 0.2≦a≦0.8, 0.1≦b≦0.4, 0≦c≦0.4 and 0≦d≦0.1), the negative electrode includes graphite as a negative electrode active material, the interlayer distance (d002) of the graphite is 0.335 nm or more and 0.338 nm or less, the one-side thickness A (μm) of the positive electrode mixture layer is 60 or more and 85 or less, the product A×B between the one-side thickness A and the density B (g/cm3) of the positive electrode mixture layer is 160 or more and 220 or less, the one-side thickness C (μm) of the negative electrode mixture layer is 40 or more and 75 or less, and the product C×D between the one-side thickness C and the density D (g/cm3) of the negative electrode mixture layer is 65 or more and 105 or less.