Gradient Crystallite Orientation in Li-Ion Negative Electrodes
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Solution Overview
Problem
The stability of negative electrodes in lithium ion secondary batteries, particularly those using natural graphite, is insufficient, leading to deteriorated cycle characteristics when the thickness of the negative electrode active material layer is increased to achieve high capacity, resulting in reduced lifespan.
Innovation Solution
A negative electrode with a thickness of 50 μm to 100 μm, where the orientation degree of the carbon material in the active material layer, measured by X-ray diffraction, is between 100 and 500, ensuring balanced conductivity and preventing excessive orientation that can lead to capacity reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness of the negative electrode active material layer is increased to achieve high capacity, then the energy density is improved, but the cycle characteristics deteriorate and stability is reduced
Solution Approach 1:
The patent applies local quality by creating a gradient in crystallite orientation throughout the electrode thickness. The inner layer (near collector) has high orientation (Lc≥100Å) for stability, while the outer layer has lower orientation (Lc<100Å) for capacity. This spatial variation in material properties resolves the contradiction between high capacity and good cycle characteristics.
Solution Approach 2:
The patent segments the negative electrode active material layer into two distinct layers: an inner layer adjacent to the current collector with specific orientation characteristics (Lc≥100Å), and an outer layer with different orientation characteristics (Lc<100Å). This segmentation allows each layer to contribute differently to overall performance, achieving both high capacity and good cycle characteristics.
2Quantity of substance
If the crystallite thickness Lc is increased to improve orientation and capacity, then the energy density is improved, but the conductivity deteriorates
Solution Approach 1:
The patent applies local quality by creating a gradient in crystallite orientation throughout the electrode thickness. The inner layer (near collector) has high orientation (Lc≥100Å) for stability, while the outer layer has lower orientation (Lc<100Å) for capacity. This spatial variation in material properties resolves the contradiction between high capacity and good cycle characteristics.
Solution Approach 2:
The patent changes the crystallite thickness parameter Lc spatially across the electrode structure. By controlling Lc to be ≥100Å in the inner layer and <100Å in the outer layer, the patent optimizes both conductivity and capacity, resolving the contradiction between these two parameters.
3Quantity of substance
If the orientation degree is increased to improve capacity, then the energy density is improved, but the structural anisotropy becomes excessive leading to stability issues
Solution Approach 1:
The patent applies local quality by creating a gradient in crystallite orientation throughout the electrode thickness. The inner layer (near collector) has high orientation (Lc≥100Å) for stability, while the outer layer has lower orientation (Lc<100Å) for capacity. This spatial variation in material properties resolves the contradiction between high capacity and good cycle characteristics.
Solution Approach 2:
The patent segments the negative electrode active material layer into two distinct layers: an inner layer adjacent to the current collector with specific orientation characteristics (Lc≥100Å), and an outer layer with different orientation characteristics (Lc<100Å). This segmentation allows each layer to contribute differently to overall performance, achieving both high capacity and good cycle characteristics.
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 enhances the cycle characteristics and stability of the battery, maintaining high energy density and preventing conductivity deterioration, thus extending the battery's lifespan.
Implementation Method 1
a negative electrode active material layer containing a negative electrode active material containing natural graphite is formed on at least one surface of a negative electrode collector
Implementation Method 2
an orientation degree A expressed as (peak intensity of carbon 002 face/peak intensity of carbon 110 face) that is a peak intensity ratio of a carbon 002 face and a carbon 110 face measured by an X-ray diffraction method
Data Source
AI summary
A battery comprising a positive electrode; a negative electrode including a negative electrode active material layer that is formed on at least one surface of a negative electrode collector; and an electrolyte, wherein in the negative electrode active material layer from the negative electrode collector up to ½ of a layer thickness in a surface direction of the negative electrode active material layer, a pore volume ratio expressed as (pore volume B/pore volume A) that is a ratio of a pore volume A (ml/g) in a range of 0.001 μm or more and 0.4 μm or less of a pore diameter measured by a mercury porosimeter and a pore volume B (ml/g) in a range of 0.4 μm or more and 10 μm or less of the pore diameter is 1.4 or more and 3.4 or less.