Silicon-Graphite Secondary Battery Composition for Swelling Control
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Solution Overview
Problem
Silicon-based materials used in secondary batteries experience significant swelling during use, leading to deterioration of cycle performance and limiting their application in commercial products.
Innovation Solution
A secondary battery design incorporating layered lithium nickel cobalt manganese oxide and layered lithium nickel cobalt aluminum oxide as positive active materials, combined with silicon-oxygen compound and graphite as negative active materials, with specific A/B value and voltage U ranges, to enhance energy density and cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used as negative active material to increase energy density, then the theoretical gram capacity increases significantly, but the swelling problem deteriorates cycle performance
Solution Approach 1:
The patent uses a composite negative active material consisting of silicon-oxygen compound (SiOx) and graphite. The silicon-oxygen compound provides high capacity while graphite acts as a buffer to accommodate volume expansion, reducing swelling. This composite structure combines the advantages of both materials to achieve high energy density and good cycle performance simultaneously.
Solution Approach 2:
The patent optimizes the mass ratio of silicon-oxygen compound to graphite in the negative active material, controlling the silicon-oxygen compound content at 10-40 mass%. It also controls the A/B value (ratio of delithiation capacities at different voltage ranges) and the voltage U of the negative electrode plate within specific ranges. These parameter optimizations balance capacity and stability to resolve the contradiction.
2Quantity of substance
If the content of silicon-oxygen compound in negative active material is increased to improve energy density, then the theoretical capacity increases, but the swelling problem worsens cycle life
Solution Approach 1:
The patent precisely controls the mass percentage of silicon-oxygen compound in the negative active material within 10-40%, and optimizes the A/B value and voltage U parameters. By adjusting these parameters, the patent achieves the optimal balance between energy density and cycle life, preventing excessive swelling while maximizing capacity.
Solution Approach 2:
The composite structure of silicon-oxygen compound and graphite allows the system to achieve high energy density through the silicon-oxygen compound while the graphite component maintains structural integrity over cycling, extending cycle life despite the presence of swelling-prone silicon-based material.
3Reliability
If the A/B value and voltage U are optimized to improve cycle performance, then the stability increases, but the energy density may be limited
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: the A/B value (ratio of delithiation capacities), the voltage U of the negative electrode plate, and the silicon-oxygen compound content. This multi-parameter optimization enables the system to achieve both high cycle performance and high energy density by finding the optimal operating window where both requirements are satisfied.
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 higher energy density, initial coulombic efficiency, and improved cycle performance by optimizing the storage and stability of active lithium ions and maintaining the stability of the solid electrolyte interface, thereby extending the battery's lifespan.
Implementation Method 1
The non-lithium negative electrode and the positive electrode are lithium ion permeable
Implementation Method 2
A respective microporous polymer separator is disposed between the lithium source electrode and each of the negative and positive electrodes
Data Source
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AI summary
The present application provide a secondary battery and related battery module, battery pack and apparatus. The secondary battery includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the secondary battery includes a positive active material selected from one or more of layered lithium nickel cobalt manganese oxide and layered lithium nickel cobalt aluminum oxide, and a negative active material including graphite and silicon-oxygen compound; when a button battery made from the negative electrode plate and a lithium metal sheet is subjected to constant-current lithium intercalation at a rate of 0.1C to a voltage of 0.005V, and then subjected to constant-current lithium intercalation at a rate of 0.05C to a voltage of 0.005V, and then subjected to constant-current lithium deintercalation at a rate of 0.1C to a voltage of 1.2V, the delithiation capacity A of the negative electrode film in the voltage range of 0.005V to the delithiation platform voltage and the delithiation capacity B of the negative electrode film in the voltage range of the delithiation platform voltage to 1.2V satisfy: 1 ≤A/B≤2; and when the secondary battery is discharged to a voltage of 2.5V, the voltage U of the negative electrode plate relative to a lithium metal reference electrode satisfies: 0.5≤U≤0.7V.