SiOx Composite Anode Material With Carbon Coating for Cycle Life
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Solution Overview
Problem
Current lithium secondary batteries face issues with reduced initial efficiency and service life due to the reaction of silicon-based particles with lithium ions, leading to the formation of lithium silicates and volume changes during charging/discharging, which affects conductivity and capacity retention.
Innovation Solution
A negative electrode active material is developed using silicon-based composite particles with a Mg or Li compound and a carbon layer, optimizing the BET specific surface area and powder conductivity to improve initial efficiency and service life, comprising silicon-based composite particles with a BET specific surface area of 5-60 m2/g and a carbon layer with a conductivity of 0.05-1 S/cm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based particles are used as negative electrode active material, then discharge capacity is improved, but initial efficiency is reduced due to formation of lithium silicates
Solution Approach 1:
The patent uses silicon-based composite particles comprising SiOx (0 < x < 2) as the core material, which combines silicon's high capacity with oxide stability. This composite structure prevents complete conversion to lithium silicate while maintaining high discharge capacity, thereby improving both capacity and initial efficiency simultaneously
Solution Approach 2:
The patent optimizes the BET specific surface area to within 60 m2/g and controls the powder density to within 1.8 g/cc. By adjusting these physical parameters, the reaction kinetics are improved while controlling side reactions, resolving the contradiction between capacity and initial efficiency
2Quantity of substance
If silicon-based particles undergo volume change during charging/discharging, then discharge capacity is improved, but conductivity is reduced
Solution Approach 1:
The patent maintains powder density within 1.8 g/cc by controlling particle morphology and density. This parameter optimization ensures good particle packing and electrical contact in the electrode, maintaining conductivity even as capacity increases through silicon-based reactions
Solution Approach 2:
The use of SiOx composite particles provides a more stable structural framework compared to pure silicon. The oxide component maintains structural integrity during volume changes, preserving electrical pathways and conductivity while still enabling high capacity lithium insertion/extraction
3Reliability
If metal doping is applied to silicon-based particles, then initial efficiency is improved, but capacity per weight is reduced
Solution Approach 1:
Instead of metal doping, the patent uses SiOx composite particles where the oxide component itself provides stability and prevents harmful side reactions. This approach improves initial efficiency without introducing heavy metal atoms that would reduce capacity per weight, as the oxygen atoms in SiOx contribute minimally to mass but significantly to stability
4Productivity
If BET specific surface area is increased, then reaction activity is improved, but service life is reduced due to increased side reactions with electrolyte
Solution Approach 1:
The patent optimizes BET specific surface area to within 60 m2/g, finding the optimal balance point. This controlled surface area provides sufficient reaction activity for good productivity while limiting the total surface available for harmful side reactions with the electrolyte, thereby extending service life
Solution Approach 2:
The patent creates particles with heterogeneous surface properties through the SiOx composite structure, where different regions have different reactivities. This local quality variation allows high reaction activity in lithium-insertion regions while reducing side reactions in oxide-stabilized regions, improving both productivity and service life
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 enhances the initial efficiency and service life of lithium secondary batteries by reducing side reactions with the electrolyte and maintaining conductivity, thereby improving discharge capacity and cycle performance.
Implementation Method 1
the negative electrode active material has a powder conductivity of 0.05 S/cm to 1 S/cm
Implementation Method 2
a negative electrode active material for intercalating and de-intercalating lithium ions from the positive electrode
Data Source
AI summary
A negative electrode active material including silicon-containing composite particles including SiOx (0<x<2) and a Mg compound or Li compound; and a carbon layer present on a surface of the silicon-containing composite particles. The silicon-containing composite particles have a BET specific surface area of 5 m2/g to 60 m2/g, and the negative electrode active material has a BET specific surface area of 2 m2/g to 15 m2/g, and a powder conductivity of 0.05 S/cm to 1 S/cm at a powder density of 1.4 g/cc. A negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method for preparing the negative electrode active material are also disclosed.