Si-Ti Alloy Negative Electrode for Li-Ion Batteries
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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 with a predetermined composition (Si x Ti y M z A a) and a current collector with elastic elongation greater than 1.30% is employed, which suppresses amorphous-crystal phase transitions and accommodates 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 silicon 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.
Solution Approach 2:
The patent creates a composite structure by forming an amorphous silicon alloy through mechanical alloying of silicon powder with other elements. This composite approach combines the high capacity benefit of silicon with the structural stability of an amorphous matrix, achieving both high energy density and improved cycle durability.
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 charge-discharge capacity
Solution Approach 1:
The patent fundamentally changes the active material parameter from carbon/graphite to amorphous silicon alloy. This parameter change enables the negative electrode to achieve both high capacity (exceeding 372 mAh/g theoretical limit of graphite) and good cycle life by utilizing the amorphous structure's ability to accommodate volumetric changes during lithium insertion-extraction.
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, capable of maintaining high discharge capacity retention rates, suitable for vehicle power sources.
Implementation Method 1
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. The negative electrode active material is an alloy represented by the following formula (1). In addition, elastic elongation of the current collector is 1.30% or greater.
Implementation Method 2
1 mole of a Si material absorbs and releases 4.4 moles of lithium ions, in accordance with the following reaction formula (A), during charge and discharge
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): 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 elastic elongation of the current collector is 1.30% or greater.