Carbon-Coated SiOx Anode Material for Stable Aqueous Slurry Processing
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Solution Overview
Problem
The existing negative electrode active materials for lithium-ion secondary batteries, particularly those using silicon compounds, face challenges with stability in aqueous slurries, leading to limited improvement in battery characteristics due to lithium doping methods that result in the removal of doped lithium, reducing the battery's capacity retention and initial efficiency.
Innovation Solution
A negative electrode active material is developed with silicon compound particles (SiOx: 0.5≤x≤1.6) coated with carbon and incorporating Li2SiO3 and Li2Si2O5, ensuring specific intensity ratios and NMR peak characteristics to maintain stability and prevent gas generation, thereby enhancing capacity retention and initial efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon compound particles are doped with lithium to improve battery initial efficiency and cycle characteristics, then battery capacity is improved, but the doped lithium is removed during washing, reducing capacity retention and initial efficiency
Solution Approach 1:
The patent uses a specific washing solution containing lithium hydroxide and lithium carbonate as an intermediary medium to perform washing without removing doped lithium. This washing solution acts as a bridge that maintains lithium content while removing other impurities, resolving the contradiction between washing cleanliness and lithium retention.
Solution Approach 2:
The patent changes the parameters of the washing process by specifying precise concentrations of lithium hydroxide (0.01-10 wt%) and lithium carbonate (0.01-10 wt%) in the washing solution, along with controlled washing time (1-48 hours). These parameter adjustments ensure that doped lithium is retained while achieving effective cleaning.
2Reliability
If silicon oxide is doped with lithium to improve battery characteristics, then initial efficiency increases, but the lithium compound dissolves in water causing hydrogen gas generation and coating failure
Solution Approach 1:
The patent employs a specially formulated washing solution as an intermediary that prevents direct contact between water and the lithium-containing silicon compound. This intermediary medium allows washing to proceed without causing hydrogen gas generation or coating failure, while still achieving the desired cleaning effect.
Solution Approach 2:
The patent applies preliminary anti-action by pre-treating the silicon oxide with lithium doping to create a stable structure that resists water dissolution. The controlled lithium incorporation creates a compound that is stable in aqueous environments, preventing the harmful effects of hydrogen gas generation and coating failure during subsequent washing processes.
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 provides a negative electrode active material that significantly improves the stability and performance of lithium-ion secondary batteries by maintaining high capacity retention and initial efficiency, ensuring industrial applicability and favorable battery characteristics.
Implementation Method 1
Use of silicon as a main material of a negative electrode active material, however, expands and shrinks the negative electrode active material when charging or discharging, thereby making the negative electrode active material easy to break particularly near its surface layer.
Implementation Method 2
The breakage of the surface layer of the negative electrode active material creates a new surface, increasing a reaction area of the active material. The new surface then causes the decomposition reaction of an electrolyte and is coated with a decomposition product of the electrolyte, thereby consuming the electrolyte.
Implementation Method 3
this silicon compound in the lithium compound dissolves in water, exhibiting basicity. Consequently, the reaction with the silicon compound causes hydrogen gas generation.
Implementation Method 4
the negative electrode active material particles are at least partially coated with a carbon material
Implementation Method 5
the negative electrode active material particles satisfy Ib/Ia≤4.8 and Ic/Ia≤6.0 in an X-ray diffraction measurement using a Cu-Kα line
Data Source
AI summary
The inventive negative electrode active material for a non-aqueous electrolyte secondary battery contains negative electrode active material particles which include silicon compound (SiOx: 0.5≤x≤1.6) particles. The negative electrode active material particles are at least partially coated with a carbon material, contain one or more selected from Li2SiO3 and Li2Si2O5, and satisfy Ib/Ia≤4.8 and Ic/Ia≤6.0 in an X-ray diffraction measurement using a Cu-Kα line. Ia represents an intensity of a peak around 2θ=28.4° attributable to Si obtained by the X-ray diffraction. Ib represents a peak intensity of a peak attributable to Li2SiO3 obtained by the X-ray diffraction. Ic represents a peak intensity of a peak attributable to Li2Si2O5 obtained by the X-ray diffraction. Thus, the present invention provides a negative electrode active material for a non-aqueous electrolyte secondary battery, which is stable over a long period even in an aqueous slurry and enables high capacity, favorable cycle characteristics and first-time efficiency.