Negative Electrode Carbon Gradient for Low Self-Discharge Batteries
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Solution Overview
Problem
Lithium ion batteries using titanium oxide as a negative electrode active material face issues with self-discharge when stored for long periods, due to the high electro-conductivity of carbon materials regardless of the state of charge (SOC) of the titanium oxide.
Innovation Solution
A battery design is implemented where the negative electrode active material-containing layer includes a niobium-titanium composite oxide and a conductive agent with a carbon material, with a specific carbon content ratio gradient to reduce surface conductivity while maintaining internal electron conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon material is added as conductive agent to improve electron conductivity, then electron conductivity is improved, but self-discharge increases during long-term storage
Solution Approach 1:
The patent applies local quality by creating a carbon content ratio gradient within the negative electrode active material-containing layer. The carbon content varies with depth from the principal surface, with higher carbon content near the surface to improve electron conductivity and lower carbon content deeper inside to reduce self-discharge during storage. This gradient structure allows different regions to have optimized properties for their specific functions.
Solution Approach 2:
The patent introduces a depth dimension to the carbon distribution problem. Instead of uniform carbon distribution, it establishes a three-dimensional carbon content ratio gradient where the carbon content ratio C2/C1 (where C2 is carbon content at depth 0.5A and C1 is carbon content at depth 1μm) satisfies 2≤C2/C1≤30. This dimensional approach allows simultaneous optimization of surface conductivity and bulk stability.
2Reliability
If uniform carbon distribution is used to maintain conductivity, then electron conductivity is maintained, but self-discharge cannot be prevented
Solution Approach 1:
The patent replaces uniform carbon distribution with a spatially varying carbon content ratio gradient. The carbon content is locally optimized at different depths: higher concentration near the principal surface for conductivity, and lower concentration deeper in the layer to minimize self-discharge. This local differentiation resolves the contradiction between maintaining conductivity and preventing self-discharge.
Solution Approach 2:
The patent changes the parameter of carbon content distribution from uniform to gradient-based. By controlling the carbon content ratio C2/C1 to satisfy 2≤C2/C1≤30, it transforms the homogeneous parameter distribution into a controlled gradient, allowing the system to achieve both high conductivity and low self-discharge through parameter optimization.
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 effectively prevents self-discharge during long-term storage by managing the carbon content ratio gradient within the negative electrode active material-containing layer, thereby maintaining battery capacity.
Implementation Method 1
when lithium is inserted therein, the valence of Ti changes from tetravalent to trivalent and the valence of Nb changes from pentavalent to trivalent, so that the charge is compensated
Implementation Method 2
a conductive agent that includes a carbon material
Data Source
AI summary
According to one embodiment, a battery is provided. The battery includes a positive electrode, and a negative electrode including a negative electrode active material-containing layer including a niobium-titanium composite oxide and a conductive agent that includes a carbon material. The negative electrode active material-containing layer includes a principal surface facing the positive electrode. Assuming that the thickness of the negative electrode active material-containing layer is A, a ratio (C2/C1) of carbon content ratio C2 at a depth of 0.5 A from the principal surface to carbon content ratio C1 at a depth of 1 μm from the principal surface satisfies 2≤C2/C1≤30.