Silicon Nanoparticle Anode Material With SiC4 Matrix Embedding
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Solution Overview
Problem
Silicon nanoparticles used as negative electrode materials in lithium ion secondary batteries face issues such as volume expansion leading to mechanical destruction, spatial/electrical isolation, and increased specific surface area causing irreversible capacity generation and decreased cycle life, despite efforts to improve charge/discharge characteristics through two-dimensional structures and chemical treatments.
Innovation Solution
Silicon nanoparticles with specific size and shape characteristics (70 to 300 nm in length and 15 to 70 nm in thickness) embedded in a silicon inorganic compound with SiC4 bond structural units, achieving a balanced charge/discharge performance and reducing volume change during cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If silicon particles are reduced to nanoparticle size to avoid mechanical destruction, then mechanical stability is improved, but spatial/electrical isolation occurs causing decreased battery life
Solution Approach 1:
The patent combines silicon nanoparticles with conductive carbon materials (graphene, carbon nanotubes, or conductive polymers) to form a composite structure. The conductive matrix merges with silicon particles to provide continuous electrical pathways, preventing isolation while maintaining the mechanical stability benefits of nanoparticle size.
Solution Approach 2:
The conductive carbon material acts as an intermediary between isolated silicon nanoparticles, providing electrical connectivity and mechanical support. This intermediary network allows charge transport without requiring direct contact between silicon particles, solving the isolation problem.
2Stability of the object's composition
If silicon particles are reduced to nanoparticle size, then mechanical destruction is avoided, but specific surface area increases causing irreversible capacity and decreased cycle life
Solution Approach 1:
The patent employs thin carbon coating layers or encapsulation structures around silicon nanoparticles. These flexible carbon shells protect the high-surface-area silicon particles while providing a stable interface with the electrolyte, reducing SEI formation and irreversible capacity loss.
Solution Approach 2:
The invention creates composite materials where silicon nanoparticles are integrated with conductive carbon matrices. This composite structure leverages the high capacity of silicon while the carbon component provides structural stability and reduces surface-related side reactions.
3Productivity
If scaly or flaky silicon structures are used, then charge/discharge characteristics are improved, but carbon coating is required which allows electrolyte penetration and SEI formation
Solution Approach 1:
The patent applies different properties to different parts of the silicon structure. Conductive carbon materials are selectively applied to specific regions (surfaces, interfaces, or as inter-particle connectors) rather than uniform coating, providing local conductivity enhancement without creating continuous pathways for electrolyte penetration.
4Shape
If layered silicon compounds are used, then structure is obtained, but perfect dissociation is difficult leaving large particles and impurities
Solution Approach 1:
The patent segments the layered silicon compound into smaller, more uniform units through controlled processing. The final structure consists of fine silicon particles or nanosheets rather than large layered aggregates, achieving both the desired shape characteristics and manufacturing precision.
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 enhanced charging/discharging capacities, initial Coulombic efficiency, and cycle characteristics by controlling the morphology and surface state of silicon nanoparticles, preventing collapse and minimizing the formation of the solid electrolyte interface.
Implementation Method 1
Silicon (Si) is capable of forming an alloy (an intermetallic compound) with metallic lithium and thus can electrochemically adsorb and release lithium ions
Implementation Method 2
Silicon (Si) is capable of forming an alloy (an intermetallic compound) with metallic lithium and thus can electrochemically adsorb and release lithium ions
Implementation Method 3
silicon significantly changes its volume by a magnitude of three to four times when it adsorbs and releases lithium ions
Implementation Method 4
Consequently, silicon is collapsed into fine powder by repeatedly expanding and contracting during charging and discharging cycles
Data Source
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AI summary
Silicon nanoparticles are obtained which significantly contribute to enhancing the performance of negative electrode active materials. A negative electrode active material is obtained which allows a battery to attain excellent charging/discharging capacities, high initial Coulombic efficiency and good capacity retention after charging and discharging repetitions. The present invention pertains to silicon nanoparticles for negative electrode active material in lithium ion secondary batteries in which the silicon nanoparticles have a 29Si-NMR peak which has a half width of 20 ppm to 50 ppm centered at -80 ppm and is broad ranging from 50 ppm to -150 ppm, and the silicon nanoparticles have a length in the major axis direction of 70 to 300 nm and a thickness of 15 to 70 nm or less. The present invention also pertains to a negative electrode active material for lithium ion secondary batteries that includes the silicon nanoparticles and a silicon inorganic compound in which the silicon nanoparticles are embedded, the silicon inorganic compound having a 29Si-NMR peak assigned to SiC4 bond structural units and having an equivalent composition ratio [SiC4 bonds/(SiC4 bond structural units + D units (SiO2C2) + T units (SiO3C) + Q units (SiO4))] in the range of 0.05 to 0.55. The present invention also pertains to a negative electrode for lithium ion secondary batteries including the negative electrode active material, and to a lithium ion secondary battery including the negative electrode.