Doped Silicon-Graphite Anode Composition for Low-Resistance Cycling
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Solution Overview
Problem
High Si content negative electrodes in secondary batteries face issues with increased resistance leading to decreased input-output characteristics and capacity due to expansion and shrinkage during charging and discharging, which can result in disconnection of the conduction path and reduced cycle life.
Innovation Solution
Incorporating graphite particles and Si-containing particles doped with elements from Group 15 and 16 into the negative electrode active material layer, with a specific weight ratio of 9:1 to 4:6, to suppress expansion and shrinkage, thereby improving input-output characteristics and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high Si content is used in the negative electrode active material, then the battery capacity increases, but the resistance increases leading to decreased input-output characteristics
Solution Approach 1:
The negative electrode uses a composite structure combining Si-containing particles (5-30 wt%) with graphite particles and conductive carbon particles. The Si-containing particles provide high capacity while the graphite and conductive carbon matrix maintains conductivity and structural integrity, resolving the contradiction between capacity and input-output characteristics
Solution Approach 2:
The Si-containing particles undergo doping treatment with Group 15 elements (P, As, Sb) at concentrations of 0.01-5 at%, which modifies the electrical and mechanical properties of silicon. This parameter change reduces resistance and suppresses expansion/shrinkage, thereby improving input-output characteristics while maintaining high capacity
2Quantity of substance
If high Si content is used in the negative electrode active material, then the battery capacity increases, but Li precipitation occurs reducing cycle life
Solution Approach 1:
The composite structure of Si-containing particles embedded in a graphite-conductive carbon matrix provides buffered volume expansion and maintains continuous Li-ion transport pathways. This prevents Li precipitation during cycling while preserving the high capacity benefits of silicon
Solution Approach 2:
Doping Si with Group 15 elements modifies the crystal structure and mechanical properties, suppressing the extreme expansion and shrinkage that lead to particle disintegration and Li precipitation. This parameter modification extends cycle life while maintaining capacity
3Reliability
If only doped silicon is used as the negative electrode active material, then the resistance is low and input-output characteristic is high, but expansion and shrinkage at charging and discharging become large
Solution Approach 1:
The composite structure combines doped Si-containing particles with graphite and conductive carbon. The graphite and carbon matrix accommodate the volume changes of silicon during Li insertion/extraction, suppressing overall expansion and shrinkage while maintaining the low resistance and high input-output characteristics provided by the doped silicon
Solution Approach 2:
The doping of Si with Group 15 elements (0.01-5 at%) modifies the mechanical and electrical parameters of silicon, reducing its tendency for extreme expansion and shrinkage while maintaining low resistance. This enables the material to achieve both stability and high input-output performance
4Quantity of substance
If expansion and shrinkage increase during charging and discharging, then the conduction path may be disconnected, but using high Si content is needed for high capacity
Solution Approach 1:
The continuous matrix of graphite and conductive carbon particles provides a stable conduction network that remains intact during Si expansion and shrinkage. This composite structure maintains both high capacity from the Si component and reliable conduction path integrity through the graphite-carbon matrix
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 combination of graphite and doped Si-containing particles enhances conductivity and reduces expansion and shrinkage, maintaining the integrity of the conduction path and improving both input-output and cycle characteristics of the secondary battery.
Implementation Method 1
Si of the Si-containing particle is doped with an element M. The element M is at least one kind of element among elements belonging to Group 15 and Group 16 in the periodic table.
Implementation Method 2
The negative electrode active material layer includes graphite particles and Si-containing particles as a negative electrode active material
Data Source
AI summary
A secondary battery disclosed herein includes an electrode body including a positive electrode and a negative electrode. The negative electrode includes a negative electrode active material layer. The negative electrode active material layer includes graphite particles and Si-containing particles. The Si-containing particle is a complex of Si and C, and Si is doped with an element M. The element M is at least one kind of element among elements belonging to Group 15 and Group 16 in the periodic table. The doping amount of the element M in the Si-containing particle is 0.1 at % or more and 5 at % or less. The weight ratio between the graphite particles and the Si-containing particles is 9:1 to 4:6.