Si-Ti-M Alloy Negative Electrode with Elastic Binder
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Solution Overview
Problem
Lithium ion secondary batteries using carbon/graphite-based negative electrodes struggle to achieve sufficient theoretical charge-discharge capacity and energy density for vehicle applications, while silicon-based electrodes face challenges in cycle life due to large volumetric changes during charge and discharge.
Innovation Solution
A negative electrode using a ternary Si alloy (Si-Ti-M series) with a resin binder having a specific elastic modulus range, which suppresses amorphous-crystal phase transitions and accommodates volumetric changes, enhancing both initial capacity and cycle durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based negative electrode material is used to increase capacity, then energy density is improved, but cycle life deteriorates due to large volumetric expansion
Solution Approach 1:
The patent changes the physical and chemical parameters of the silicon-based material by controlling the crystallinity (amorphous vs. crystalline state) and particle size (10 μm or less). This parameter optimization reduces volumetric expansion during charge-discharge cycles while maintaining high capacity, thereby improving cycle life without sacrificing energy density
Solution Approach 2:
The patent creates a composite structure by combining silicon-based material with specific binders and conductive agents in defined ratios. This composite approach mitigates the inherent weaknesses of pure silicon (large expansion) while preserving its high capacity advantage, achieving both improved cycle life and maintained energy density
2Reliability
If carbon/graphite-based negative electrode material is used, then cycle life is improved, but energy density deteriorates due to insufficient theoretical capacity
Solution Approach 1:
The patent fundamentally changes the active material from carbon/graphite to silicon-based material, altering the chemical composition parameter. This enables the negative electrode to achieve theoretical capacities exceeding 372 mAh/g (silicon's capacity) versus graphite's 372 mAh/g limit, thereby improving energy density while maintaining acceptable cycle life through proper material design
3Reliability
If amorphous alloy with multiple metal elements is used to suppress phase transition, then cycle property is improved, but initial capacity deteriorates
Solution Approach 1:
The patent optimizes the compositional parameters of the amorphous alloy by precisely controlling the ratios of Si, Ti, and M elements according to the formula Si x Ti y M z where x≥55, y≥5, and z≥5. This parameter optimization ensures sufficient silicon content for high initial capacity while incorporating enough Ti and M to suppress harmful phase transitions, achieving both high initial capacity and good cycle property
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 achieves a well-balanced high initial capacity and cycle durability, significantly improving the performance of lithium ion secondary batteries for vehicle applications by stabilizing the electrode structure during charge and discharge cycles.
Implementation Method 1
a battery using a material alloyed with Li for a negative electrode has higher energy density than the conventional battery using the carbon/graphite-based negative electrode material
Implementation Method 2
a negative electrode active material layer containing a negative electrode active material, an electrically-conductive auxiliary agent and a binder... the binder contains a resin having an E elastic modulus within a predetermined range
Data Source
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AI summary
There is provided a negative electrode for an electric device such as a Li ion secondary battery capable of exhibiting well-balanced characteristics of a high cycle property and a high initial capacity. The negative electrode for an electric device includes a current collector and an electrode layer containing a negative electrode active material, an electrically-conductive auxiliary agent and a binder and formed on a surface of the current collector, wherein the negative electrode active material contains an alloy represented by the following formula (1): SixTiyMzAa (in the formula (1), M is at least one metal selected from the group consisting of Ge, Sn, Zn and a combination thereof, A is inevitable impurities, and x, y, z and a represent mass percent values and satisfy the conditions of 0<x<100, 0<y<100, 0<z<100, 0≤a<0.5, and x+y+z+a=100), and the binder contains a resin having an E elastic modulus of greater than 1.00 GPa and less than 7.40 GPa.