Si-Zn-M Alloy Negative Electrode for Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries using conventional 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-Zn-M series) with a resin binder having an E elastic modulus within a specific 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
1Use of energy by moving object
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 invention 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 energy density. The amorphous structure accommodates volume changes more effectively than crystalline structures.
Solution Approach 2:
The invention creates a composite material system by combining amorphous silicon-based material with specific binders and conductive agents. This composite approach addresses the cycle life issue by providing a matrix that accommodates volume changes, while maintaining the high capacity benefits of silicon. The composite structure includes amorphous silicon particles dispersed in a binder matrix with conductive carbon material.
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 invention changes the chemical composition parameter of the negative electrode material from carbon/graphite-based to silicon-based amorphous material. This parameter change enables achievement of both high energy density (exceeding 372 mAh/g) and satisfactory cycle life, overcoming the limitations of conventional carbon-based materials which are restricted to a theoretical capacity of 372 mAh/g.
3Quantity of substance
If Si alloy with Li is used to increase capacity, then initial capacity is improved, but volumetric change increases causing particle breakage
Solution Approach 1:
The invention changes the structural parameter of the silicon-based material from crystalline to amorphous form. This parameter change allows the material to accommodate large volumetric expansions (up to 4 times) during lithium alloying without particle breakage, while maintaining high initial capacity. The amorphous structure is more tolerant of volume changes compared to crystalline structures.
Solution Approach 2:
The invention employs a binder system that provides beforehand cushioning support to the amorphous silicon-based particles during volumetric expansion. The binder matrix accommodates the expansion stress, preventing particle breakage before it occurs, thereby maintaining particle integrity and electrical connectivity throughout charge-discharge cycles.
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 Si-Zn-M series alloy with a suitable resin binder achieves a well-balanced high initial capacity and cycle durability, effectively addressing the limitations of conventional materials by preventing particle breakage and extending cycle life.
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
1 mole of a Si material absorbs and releases 4.4 moles of lithium ions, in accordance with the following reaction formula (1), during charge and discharge
Implementation Method 3
A 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 having an E elastic modulus within a predetermined range
Implementation Method 4
which suppresses amorphous-crystal phase transitions and accommodates volumetric changes
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): 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 the binder contains a resin having an E elastic modulus of greater than 1.00 GPa and less than 7.40 GPa.