SiOx Negative Electrode Material for High-Capacity Cycle-Stable Li-Ion Cells
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Solution Overview
Problem
Lithium ion secondary batteries using silicon-based active materials face challenges in achieving battery capacity and cycle characteristics comparable to those using carbon-based materials, with issues such as irreversible capacity due to silicon dioxide reactions and structural instability during charge/discharge.
Innovation Solution
A negative electrode active material comprising silicon compounds (SiO x :0.5≤x≤1.6) with specific chemical shift values from 29< Si-MAS-NMR spectrum, including Li 2 SiO 3 and Li 4 SiO 4, and a mixed active material with carbon-based components, optimized to reduce irreversible capacity and improve stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as the negative electrode active material to increase battery capacity, then the theoretical capacity increases significantly (10 times or more compared to graphite), but the active material expands and contracts during charge/discharge causing structural breakdown and degraded cycle characteristics
Solution Approach 1:
The silicon-based active material is divided into fine particles with a median diameter of 15 μm or less, which reduces the expansion and contraction stress during charge/discharge cycles. This segmentation prevents structural breakdown while maintaining high capacity, resolving the contradiction between capacity improvement and cycle stability.
Solution Approach 2:
The invention uses composite silicon compounds (SiOx where 0.5 ≤ x ≤ 1.6) that combine silicon with oxygen to form a more stable structure. The presence of oxygen reduces the expansion/contraction magnitude compared to pure silicon, thereby improving cycle characteristics while maintaining high capacity through the silicon component.
2Quantity of substance
If the superficial layer of the negative electrode active material breaks during charge/discharge, then the reaction area increases and battery capacity improves, but the electrolytic solution is consumed through decomposition reactions and cycle characteristics degrade
Solution Approach 1:
A protective coating is formed on the surface of the silicon-based active material particles before they are put into service. This preliminary protective layer prevents direct contact between the electrolytic solution and the silicon surface, thereby preventing decomposition reactions and electrolyte consumption while still allowing lithium ion transport.
Solution Approach 2:
The protective coating acts as an intermediary layer between the silicon-based active material and the electrolytic solution. It mediates the interaction by allowing lithium ions to pass through while blocking harmful decomposition reactions, thus preventing electrolyte consumption without hindering the reaction area's functionality.
3Reliability
If silicon compounds with high oxygen content are used to improve structural stability, then cycle characteristics improve, but irreversible capacity increases due to reactions between silicon dioxide and lithium
Solution Approach 1:
The invention optimizes the oxygen content parameter by controlling the SiOx composition where 0.5 ≤ x ≤ 1.6. This parameter optimization balances structural stability (provided by oxygen) with reversible capacity (maintained by limiting excessive oxygen that would form SiO2). The specific compositional range achieves both stability and minimal irreversible capacity.
Solution Approach 2:
The protective coating is applied specifically to the surface region of the silicon particles, providing local stability where it is most needed (at the interface with electrolyte) without affecting the bulk silicon's high capacity characteristics. This localized approach maintains overall structural stability while preserving reversible capacity.
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 negative electrode with high capacity, excellent cycle characteristics, and improved initial charge/discharge efficiency, enhancing the performance of lithium ion secondary batteries.
Implementation Method 1
since the negative electrode active material expands and contracts during charge/discharge, mainly the neighborhood of a superficial layer of the negative electrode active material tends to be broken
Implementation Method 2
an ionic substance is generated inside the active material, and the negative electrode active material tends to be broken
Implementation Method 3
since a decomposition reaction of an electrolytic solution occurs on the new surface and a film that is a decomposition product of the electrolytic solution is formed on the new surface
Data Source
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AI summary
The present disclosure is a negative electrode active material containing particles of negative electrode active material, the particles of negative electrode active material includes: particles of silicon compound containing a silicon compound (SiOx:0.5≤x≤1.6), and wherein the particles of silicon compound have, as chemical shift values obtained from a 29Si-MAS-NMR spectrum, an intensity A of a peak derived from amorphous silicon obtained in -40 to -60ppm, an intensity B of a peak derived from silicon dioxide obtained in the vicinity of -110ppm, and an intensity C of a peak derived from Si obtained in the vicinity of -83ppm, which satisfy the following formula 1 and formula 2. Thus, when used as the negative electrode active material of a lithium ion secondary battery, a negative electrode active material capable of increasing battery capacity and improving the cycle characteristics and initial charge/discharge characteristics is provided. B≤1.5×A B<C