Si-Zn Alloy Negative Electrode for Li-Ion Battery Cycle Life
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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 with cycle life due to large volumetric changes during charge and discharge.
Innovation Solution
A negative electrode using a ternary Si alloy with a specific composition (Si x Zn y M z A a) and a current collector with elastic elongation greater than 1.30% is employed, where M is Sn and A represents inevitable impurities, to suppress amorphous-crystal phase transitions and accommodate volumetric changes, enhancing both 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-shrinkage
Solution Approach 1:
The patent changes the physical state parameter of the silicon-based negative electrode material from crystalline to amorphous form. This parameter change suppresses the large volumetric expansion-shrinkage that occurs during charge-discharge cycles, thereby improving cycle life while maintaining high capacity. The amorphous structure allows for more flexible accommodation of lithium ions without the rigid phase transitions that cause mechanical degradation in crystalline silicon.
2Reliability
If carbon/graphite-based negative electrode material is used to ensure cycle life, then reliability is improved, but energy density deteriorates due to insufficient theoretical capacity
Solution Approach 1:
The patent employs a composite material approach by using silicon-based negative electrode material in an amorphous state, combining the high capacity advantage of silicon with the structural flexibility needed for long cycle life. This composite strategy at the material structure level (amorphous rather than crystalline) achieves both high energy density and improved reliability simultaneously.
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 lithium ion secondary battery with improved initial capacity and cycle durability, effectively balancing high energy density and long-term reliability suitable for vehicle power sources.
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 current collector having a predetermined elastic elongation
Data Source
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AI summary
[TECHNICAL PROBLEM] 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. [SOLUTION TO PROBLEM] The negative electrode for an electric device includes a current collector and an electrode layer containing a negative electrode active material, a 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): SixZnyMzAa (in the formula (1), M is at least one metal selected from the group consisting of V, Sn, Al, C 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 elongation (δ) in the electrode layer satisfies 1.29%<δ<1.70%.