Secondary Battery Negative Electrode Gradient Structure
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Solution Overview
Problem
Current secondary batteries face challenges in achieving better kinetic performance and longer cycle life while maintaining higher energy density, as existing technologies struggle to optimize the electrochemical performances of their components.
Innovation Solution
The secondary battery design incorporates a negative electrode plate with a first and second negative electrode film, where the first film contains natural graphite with a specific powder resistivity and the second film contains artificial graphite, optimized to match active sites and particle size distributions, creating a gradient pore distribution for improved electrolyte infiltration and ion conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer negative electrode structure is used, then the device complexity is low, but the kinetic performance and cycle life are insufficient
Solution Approach 1:
The negative electrode is divided into two distinct layers: a first negative electrode layer containing natural graphite particles and a second negative electrode layer containing artificial graphite particles. This segmentation allows each layer to contribute different properties - natural graphite provides good kinetic performance while artificial graphite enhances cycle life, resolving the contradiction between reliability and structural complexity.
Solution Approach 2:
Different regions of the negative electrode are assigned different material compositions and particle size distributions. The first layer uses natural graphite with specific particle characteristics optimized for kinetic performance, while the second layer uses artificial graphite with different characteristics optimized for cycle life. This local differentiation enables simultaneous improvement of both performance metrics without requiring complex overall structure.
2Reliability
If natural graphite with high powder resistivity is used, then the cycle life is improved, but the kinetic performance deteriorates
Solution Approach 1:
The patent applies local quality by assigning different graphite types to different layers. The first layer contains natural graphite with lower powder resistivity (0.5-2.0 mΩ·cm) optimized for fast ion diffusion and kinetic performance. The second layer contains artificial graphite with higher powder resistivity (2.0-5.0 mΩ·cm) optimized for cycle life. This spatial differentiation of material properties resolves the contradiction between speed and reliability.
Solution Approach 2:
The negative electrode uses a composite structure combining two types of graphite materials with different resistivity characteristics. This composite approach allows the electrode to simultaneously exhibit fast ion diffusion (from natural graphite layer) and long cycle life (from artificial graphite layer), resolving the contradiction between kinetic performance and reliability.
3Speed
If the negative electrode active material particles are made smaller to improve ion diffusion, then the kinetic performance is improved, but the energy density decreases
Solution Approach 1:
The patent implements local quality by differentiating particle size distributions between layers. The first negative electrode layer contains particles with Dv50 of 15-25 μm optimized for fast ion diffusion, while the second layer contains particles with Dv50 of 5-15 μm. This gradient particle size distribution allows smaller particles (faster diffusion) to be concentrated where they provide maximum kinetic benefit, while larger particles contribute more to energy density, resolving the contradiction between speed and quantity.
Solution Approach 2:
The patent resolves the particle size contradiction by transitioning from a single-dimensional particle size optimization to a two-dimensional solution: differentiating both particle size and material type across layers. This dimensional approach allows simultaneous optimization of ion diffusion (through smaller particles in first layer) and energy density (through larger particles in second layer), as each layer operates in its optimized parameter space.
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 design enhances kinetic performance, cycle life, and energy density by ensuring better ion diffusion and reduced lithium precipitation, leading to improved safety and capacity retention.
Implementation Method 1
active ions are intercalated into and deintercalated from the positive electrode plate and the negative electrode plate therebetween back and forth
Implementation Method 2
The electrolyte conducts active ions between the positive electrode plate and the negative electrode plate
Implementation Method 3
creating a gradient pore distribution for improved electrolyte infiltration
Data Source
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AI summary
The present application relates to a secondary battery, a method for manufacturing the same and an apparatus containing the same. Specifically, in the secondary battery of the present application, a negative electrode film comprises a first negative electrode film and a second negative electrode film, the first negative electrode film is disposed on at least one surface of the negative electrode current collector and comprises a first negative electrode active material, the second negative electrode film is disposed on the first negative electrode film and comprises a second negative electrode active material. The first negative electrode active material comprises natural graphite and satisfies: 6 mΩ•cm ≤ A ≤ 12 mΩ•cm, the second negative electrode active material comprises artificial graphite and satisfies: 13 mΩ•cm ≤ B ≤ 20 mΩ•cm, A is a powder resistivity of the first negative electrode active material tested at a pressure of 8 Mpa, and B is a powder resistivity of the second negative electrode active material tested at a pressure of 8 Mpa. The secondary battery of the present application can have better kinetic performance and longer cycle life while maintaining higher energy density.