SiOx-Carbon Negative Electrode and Solid Solution Positive Electrode for High Capacity Batteries
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Solution Overview
Problem
Lithium ion secondary batteries using a negative electrode with SiOx and carbon materials face challenges in achieving high capacity and cycle durability due to the limitations of carbon-graphite based electrodes and the instability of silicon oxide materials, leading to issues with rate performance and irreversible capacity.
Innovation Solution
A lithium ion secondary battery design incorporating a negative electrode active material layer with a Si-containing alloy and carbon, combined with a positive electrode using a solid solution positive electrode active material doped with specific elements, where the coating amount of the negative electrode active material layer is controlled between 3 to 11 mg/cm², optimizing the composition and structure to enhance capacity and cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If carbon-graphite based negative electrode material is used, then charge and discharge cycle life is improved, but theoretical charge and discharge capacity cannot be ensured
Solution Approach 1:
The patent uses a composite negative electrode material consisting of SiOx (silicon oxide) and carbon. The SiOx component provides high theoretical capacity (4200 mAh/g for Si) while the carbon component ensures cycle life and structural stability. This composite approach allows the battery to achieve both high capacity and good cycle performance by combining the advantages of different materials.
2Quantity of substance
If SiOx negative electrode material is used, then theoretical capacity is improved, but irreversible capacity is generated during initial Li absorption
Solution Approach 1:
The patent optimizes the composition parameters of the SiOx material, specifically controlling the oxygen content and phase structure. By adjusting these parameters, the material achieves a balance between high capacity and reduced irreversible capacity loss during initial charging.
3Quantity of substance
If Si negative electrode active material is used, then capacity is improved, but volumetric expansion causes decrease in cycle life
Solution Approach 1:
The patent creates a composite structure where SiOx is combined with carbon material. The carbon component acts as a buffer that constrains the volumetric expansion of Si during lithium insertion, preventing the severe volume changes (approximately 4 times) that would otherwise cause electrode degradation and reduced cycle life.
Solution Approach 2:
The carbon matrix surrounding the SiOx particles acts as a flexible constraint structure that accommodates volume changes while maintaining electrode integrity, similar to how a flexible shell protects and contains expanding material.
4Quantity of substance
If solid solution positive electrode active material is used, then high capacity property is achieved, but rate performance is insufficient
Solution Approach 1:
The patent optimizes the particle size and morphology parameters of the solid solution positive electrode active material. By controlling these physical parameters, the material achieves both high capacity and improved rate performance, as smaller particles provide shorter diffusion paths for lithium ions while maintaining the high capacity characteristics of the solid solution structure.
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 significantly reduces initial discharge capacity losses and achieves satisfactory rate performance while maintaining high capacity, making the battery suitable for vehicle applications with improved cycle life and energy density.
Implementation Method 1
when 1 mol of Si absorbs and desorbs 4.4 mol of lithium ions in accordance with the reaction formula (A) and a reversible capacity component of Li22Si5(= Li4.4Si) with a theoretical capacity of 4200 mAh/g is generated
Implementation Method 2
a positive electrode active material layer containing a positive electrode active material... the positive electrode active material layer contains a positive electrode active material which is represented by the following formula (2)... the solid solution positive electrode active material is represented by the following formula (3)
Data Source
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AI summary
To provide a means for sufficiently utilizing a high capacity characteristic of a solid solution positive electrode active material and capable of achieving satisfactory performance of a rate characteristic in an electrical device such as a lithium ion secondary battery containing a positive electrode using the solid solution positive electrode active material. An electrical device has a power generating element containing a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a surface of a negative electrode current collector, and a separator. The coating amount of the negative electrode active material layer is from 3 to 11 mg/cm2, and the negative electrode active material layer contains a negative electrode active material represented by formula (1) . The positive electrode active material layer contains a positive electrode active material (solid solution positive electrode active material) represented by formula (2), and a material represented by formula (3) and having a predetermined amount of a predetermined element M on particle surfaces is used as the solid solution positive electrode active material contained in the positive electrode active material layer.