Silicon Negative Electrode Lithium Predoping for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries face challenges with high energy density and short cycle life due to electrode material expansion, shrinkage, and irreversible capacity, particularly when using silicon as a negative electrode active material, and issues with lithium distribution and deposition in existing battery designs.
Innovation Solution
A lithium ion secondary battery design where the negative electrode is doped with lithium to satisfy specific ratios of lithium insertion, release, and predoping amounts, ensuring uniform volume change and minimizing lithium deposition, using a combination of silicon and silicon oxide with carbon to enhance cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as a negative electrode active material to increase energy density, then capacity is improved, but the electrode active material expands and shrinks causing pulverization and short cycle life
Solution Approach 1:
Silicon particles are embedded within a porous carbon matrix structure, where the carbon acts as a protective container that accommodates silicon's volume expansion and contraction during charge-discharge cycles. This nested configuration prevents pulverization while maintaining high capacity.
Solution Approach 2:
The negative electrode uses a composite material system combining silicon, silicon oxide, and carbon in specific ratios. This composite structure leverages silicon's high capacity, silicon oxide's stability, and carbon's conductivity and structural integrity to achieve both high capacity and long cycle life.
2Quantity of substance
If lithium is previously provided to the negative electrode to improve energy density, then capacity is improved, but lithium deposits on the negative electrode surface causing rapid capacity decrease
Solution Approach 1:
Lithium is selectively predoped in specific regions of the negative electrode - primarily in the carbon matrix and at interfaces - rather than uniformly throughout. This localized predoping creates favorable conditions for lithium insertion without causing surface deposition that would harm capacity retention.
Solution Approach 2:
The patent optimizes the amount of predoped lithium as a controllable parameter, setting it to satisfy specific ratio relationships with the positive electrode capacity. By precisely controlling this parameter within optimal ranges, the battery achieves high energy density while preventing harmful lithium deposition.
3Quantity of substance
If the negative electrode capacity is increased to improve energy density, then energy density is improved, but uniform volume change during charge and discharge becomes difficult to maintain
Solution Approach 1:
The negative electrode composition is designed to be homogeneous in terms of lithium distribution and material distribution. The carbon matrix uniformly distributes silicon particles and predoped lithium throughout its structure, ensuring uniform volume change during charge-discharge cycles even at high 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 battery achieves improved energy density and extended cycle life with reduced irreversible capacity and lithium deposition, maintaining high performance even after repeated charge and discharge cycles.
Implementation Method 1
the use of a Li-occluding substance that forms an alloy with lithium, represented by the composition formula LixA (A comprises an element such as aluminum), as a negative electrode active material
Implementation Method 2
This negative electrode active material has a large amount of occluded and released lithium ions per unit volume and high capacity
Implementation Method 3
metal lithium foil previously affixed to a positive electrode is electrochemically diffused in the carbon material of a negative electrode
Implementation Method 4
pulverization proceeds due to the fact that the electrode active material itself expands and shrinks when lithium ions are occluded and released
Data Source
Figure 1~2
Figure 3~4
AI summary
In a lithium ion secondary battery including a positive electrode, a separator, a negative electrode, and a package body, the negative electrode includes simple substance silicon as a negative electrode active material, and a negative electrode binder, and is doped with lithium, and the following formulas (1) and (2) are satisfied: 1.2≤Ma/Mc≤1.9 1.0<Ma/Mc+MLi<1.6 wherein an amount of lithium inserted into the negative electrode until the negative electrode reaches a potential of 0.02 V with respect to metal lithium is Ma (a number of atoms), an amount of lithium released from the positive electrode until the positive electrode reaches a potential of 4.3 V with respect to metal lithium is Mc (a number of atoms), and an amount of lithium with which the negative electrode is doped is MLi (a number of atoms).