Gradient Negative Electrode for Fast Charging and Energy Density
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Solution Overview
Problem
Existing secondary lithium batteries face a trade-off between high power density and high energy density, as reducing electrode thickness to increase power density typically decreases charge storage capacity.
Innovation Solution
A negative electrode with a gradient structure, where the distal portion is designed for high power density and the proximal portion for high energy density, featuring varying particle sizes, porosity, and electrochemical reaction rates across its thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the thickness of the negative electrode is reduced to increase power density, then the power density is improved, but the charge storage capacity (energy density) deteriorates
Solution Approach 1:
The negative electrode is designed with a gradient structure where different regions have different properties: the first region (closer to current collector) has larger particles and higher energy density, while the second region (closer to separator) has smaller particles and higher power density. This local differentiation allows each region to optimize for its specific function, resolving the contradiction between overall power density and charge storage capacity.
Solution Approach 2:
The negative electrode is segmented into multiple regions with distinct characteristics rather than being uniform. The gradient structure divides the electrode into a first region with larger active material particles and a second region with smaller particles, allowing each segment to contribute differently to the overall performance - one for energy storage, the other for power delivery.
2Speed
If the thickness of the negative electrode is reduced to shorten Li+ diffusion pathway, then the charge and discharge rate is improved, but the energy density deteriorates
Solution Approach 1:
Different regions of the negative electrode have different particle sizes optimized for different functions: the second region with smaller particles provides fast charge and discharge rates by shortening Li+ diffusion pathways, while the first region with larger particles maintains high energy density. This local optimization resolves the contradiction between charge rate and energy density.
Solution Approach 2:
Instead of uniformly reducing electrode thickness in one dimension, the invention uses a gradient approach that varies particle size across the thickness dimension. This creates a dimensional transition where particle size (another dimension) is used to optimize different regions for different functions, achieving both fast charge rates and high energy density.
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 gradient structure enhances fast charging capabilities without significantly reducing charge storage capacity, improving both power and energy density performance.
Implementation Method 1
The lithium ions released from the negative electrode diffuse through the electrolyte to the positive electrode
Implementation Method 2
convert chemical energy into electrical energy by means of electrochemical reduction-oxidation (redox) reactions
Implementation Method 3
an electrolyte that provides a medium for the conduction of lithium ions between the negative and positive electrodes
Data Source
AI summary
A negative electrode of a lithium battery includes a current collector and a negative electrode layer disposed on a major surface of the current collector. The negative electrode layer exhibits a gradient structure including a proximal portion adjacent the major surface of the current collector and an opposite distal portion that defines a facing surface of the negative electrode layer. The negative electrode layer is configured such that a power density of the distal portion of the negative electrode layer is greater than that of the proximal portion of the negative electrode layer, and an energy density of the proximal portion of the negative electrode layer is greater than that of the distal portion of the negative electrode layer.