Core-Shell Negative Electrode Material for High-Capacity Batteries
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Solution Overview
Problem
Current non-aqueous electrolyte secondary batteries with carbon/graphite-based negative electrodes face limitations in achieving high discharge capacity and energy density suitable for vehicle applications, and existing solutions require high-temperature heat treatment, increasing production costs and complexity.
Innovation Solution
A non-aqueous electrolyte secondary battery negative electrode material is developed with a core-shell structure, comprising carbonaceous particles as the core and a shell of polyimide and silicon-based or tin-based active material particles, where the volume average particle size ratio and content are optimized to enhance discharge capacity without high-temperature heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon/graphite-based negative electrode material is used, then charge-discharge cycle lifetime is improved, but discharge capacity is limited to theoretical maximum of 372 mAh/g
Solution Approach 1:
The patent uses a composite structure where silicon-based negative electrode active material particles (providing high capacity) are coated with carbonaceous material (providing structural stability and conductivity). This composite approach combines the high discharge capacity of silicon (theoretical capacity up to 3600 mAh/g for Li15Si4) with the cycle lifetime advantages of carbon materials, resolving the contradiction between capacity and reliability.
2Quantity of substance
If silicon-based negative electrode active material is used, then energy density is improved, but volume expansion during charging causes reduced cycle lifetime
Solution Approach 1:
The patent employs a carbonaceous coating shell around silicon-based particles that can flexibly accommodate the volume expansion (about 4 times) and contraction during charging and discharging. This shell acts as a protective layer that maintains structural integrity despite the large volume changes of silicon, preventing electrode degradation and maintaining cycle lifetime while preserving high energy density.
Solution Approach 2:
The silicon-based particles are nested within a carbonaceous material shell, creating a core-shell structure. The inner silicon core provides high capacity while the outer carbon shell provides structural stability and conductivity. This nested configuration allows the silicon to expand and contract within the protective carbon shell, resolving the contradiction between energy density and cycle lifetime.
3Stability of the object's composition
If high-temperature heat treatment is applied to carbonaceous material, then structural stability is improved, but production cost and complexity increase
Solution Approach 1:
The patent modifies the heat treatment parameters by conducting carbonization at a relatively low temperature of 500°C or lower (compared to conventional high-temperature treatments). This parameter change is sufficient to achieve the necessary structural stability and graphitization of the carbonaceous coating while avoiding the need for complex high-temperature equipment and processes, thereby reducing production complexity and cost while maintaining structural stability.
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 solution significantly increases discharge capacity while minimizing the impact of volume changes during charging and discharging, reducing the need for high-temperature processing and associated costs, thereby improving the battery's energy density and cycle durability.
Implementation Method 1
In a carbon/graphite-based negative electrode material, since charging and discharging is achieved by intercalation and deintercalation of lithium ions in graphite crystals
Implementation Method 2
batteries having a material capable of alloying with Li used for the negative electrode exhibit increased energy densities
Implementation Method 3
the volume expansion in the case of intercalating Li ions is about 1.2 times in a graphite material, while in the Si material, when Si and Li are alloyed, an amorphous state is converted to a crystalline state, and a large volume change (about 4 times) occurs
Data Source
Figure 1
Figure 2~3
AI summary
To provide a non-aqueous electrolyte secondary battery negative electrode material that can be produced even without performing a heat treatment at a high temperature such as 2,000°C or higher and can have the discharge capacity further increased. The non-aqueous electrolyte secondary battery negative electrode material according to the invention has a core portion including carbonaceous negative electrode active material particles; and a shell portion including a polyimide and silicon-based negative electrode active material particles and/or tin-based negative electrode active material particles. There is a feature that the value of the ratio of the volume average particle size (D50) of the silicon-based negative electrode active material particles and/or tin-based negative electrode active material particles with respect to the volume average particle size (D50) of the carbonaceous negative electrode active material particles is 0.001 to 0.1, and the content of the silicon-based negative electrode active material particles and/or tin-based negative electrode active material particles with respect to 100% by mass of the content of the carbonaceous negative electrode active material particles is 2% to 20% by mass.