Silicon Negative Electrode Material with Non-Equilibrium Surface Layer
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Solution Overview
Problem
Current silicon-based negative electrodes for lithium rechargeable batteries face issues such as irreversible capacity loss, electrode expansion, and poor charge/discharge cycle properties due to reactions with the electrolyte solution, leading to reduced battery capacity and efficiency.
Innovation Solution
A negative electrode material comprising silicon particles with a surface layer of a non-equilibrium phase containing carbon or nitrogen, where the element Z is present in a concentration range that suppresses the formation of equilibrium compounds like SiC or Si3N4, reducing reactivity with the electrolyte and enhancing charge/discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si-based negative electrode material is used to increase capacity, then battery capacity is improved, but electrode expansion and reactivity with electrolyte solution worsen
Solution Approach 1:
The patent uses a composite material consisting of Si particles coated with an amorphous carbon layer. The Si particles provide high capacity while the carbon coating suppresses reactivity with electrolyte and prevents electrode expansion. This composite structure resolves the contradiction between high capacity and good cycle properties.
Solution Approach 2:
The patent applies a thin amorphous carbon film on the surface of Si particles. This thin film acts as a protective shell that suppresses the reactivity of Si with electrolyte solution and prevents volume expansion during charge/discharge cycles, while allowing Li ion diffusion. This resolves the contradiction between high capacity and electrode stability.
2Quantity of substance
If Si particles are heat treated to form SiC-free material, then capacity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent specifies precise heat treatment parameters: heating at 600-900°C for 1-24 hours in an inert or reducing atmosphere. By controlling these parameters, SiC formation is suppressed while achieving the desired amorphous carbon coating. This resolves the contradiction between high capacity and ease of manufacture by providing specific controllable parameters.
3Reliability
If nitrogen atmosphere heat treatment is applied to form SiNxOy particles, then charge/discharge cycle properties are improved, but manufacturing complexity increases
Solution Approach 1:
The patent uses nitrogen atmosphere during heat treatment to prevent oxidation and control the formation of SiNxOy particles. The nitrogen atmosphere provides an inert environment that improves charge/discharge cycle properties while being relatively easy to implement. This resolves the contradiction between improved reliability and ease of manufacture.
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 results in a high-performance battery with improved discharge capacity, charge/discharge efficiency, and suppressed electrode expansion, maintaining stability and reliability even under high-temperature conditions.
Implementation Method 1
a compound of a non-equilibrium phase in which an element Z is present in Si in a non-equilibrium state
Implementation Method 2
heat treatment of Si particles and a carbon precursor provides a negative electrode material that consists of Si and C and contains little or no SiC
Data Source
AI summary
A negative electrode material for a nonaqueous electrolyte rechargeable battery that can stably and efficiently realize a high-performance nonaqueous electrolyte rechargeable battery in which a high discharge capacity, high charge/discharge efficiency at an initial stage and during charge/discharge cycles, and excellent charge/discharge cycle properties are provided as well as electrode expansion in volume after charge/discharge cycles is suppressed. The negative electrode material for a nonaqueous electrolyte rechargeable battery in the form of particles having, at least on the surface thereof, a compound of the phase in which an element Z is present in Si in a non-equilibrium state. The compound is expressed by the general formula SiZxMy, where Z represents C and/or N, M represents an element other than C and N, and when the concentration of the element Z in a compound SiaZp, where each of a and p is an integer, having a composition closest to that of Si and present in an equilibrium state is presumed to be 100 atomic percent, the concentration of the element Z in the compound SiZxMy is in the range of 10 to 95 atomic percent, and y is in the range of 0 to 0.5.