Si-Graphite Negative Electrode for Stable Battery Capacity
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Solution Overview
Problem
High capacity negative electrode materials like Si-based compounds in nonaqueous secondary batteries experience significant volume changes during charging/discharging, leading to deteriorated battery characteristics, and existing solutions fail to effectively prevent this while maintaining capacity and safety.
Innovation Solution
A nonaqueous secondary battery design incorporating a negative electrode with a graphite carbon material and a Si-based material, combined with a positive electrode containing a lithium-containing composite oxide with specific elemental composition and sulfur content, to stabilize the negative electrode and enhance charge-discharge cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high capacity negative electrode materials containing Si are used to increase battery capacity, then the battery capacity is improved, but the battery characteristics deteriorate sharply due to significant volume changes during charging/discharging
Solution Approach 1:
The patent applies local quality by creating a composite negative electrode structure where Si-based material (high capacity) is combined with graphite carbon material (stable structure). Each material serves its local function: Si provides high capacity while graphite provides structural stability and volume change accommodation, resolving the contradiction between capacity and reliability
Solution Approach 2:
The patent uses composite materials by combining Si-based negative electrode material with graphite carbon material in a specific ratio (Si-based:graphite = 95:5 to 50:50 by mass). This composite structure allows the Si to contribute high capacity while the graphite matrix provides structural stability and buffers volume changes, simultaneously achieving both high capacity and reliable cycle characteristics
2Quantity of substance
If conventional nonaqueous secondary battery construction is used with high capacity negative electrode materials, then manufacturing simplicity is maintained, but capacity increase cannot be achieved without deteriorating battery characteristics
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratio of Si-based material to graphite carbon material (95:5 to 50:50 by mass) and controlling the particle size distribution (D50: D10 between 1.05-1.30, D90: D10 between 0.85-1.15). These parameter optimizations enable capacity increase while maintaining charge-discharge cycle characteristics without requiring fundamental construction changes
3Quantity of substance
If Si-based material is used as negative electrode active material to achieve high capacity, then the battery capacity is improved, but volume changes during charging/discharging cause deterioration of battery characteristics
Solution Approach 1:
The patent applies the counterweight principle by using graphite carbon material to balance and compensate for the volume changes of Si-based material during charging/discharging. The graphite acts as a structural buffer that absorbs and distributes the mechanical stress from Si expansion/contraction, maintaining overall electrode stability while preserving Si's high capacity benefits
Solution Approach 2:
The composite structure of Si-based material and graphite carbon material allows the graphite matrix to provide structural stability while the Si particles provide high capacity. The composite design enables the graphite to counterbalance the volume instability of Si, achieving both high capacity and volume stability 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 battery achieves high capacity, excellent safety, and improved charge-discharge cycle performance by stabilizing the negative electrode through the use of graphite carbon and a carefully formulated lithium-containing composite oxide, preventing Mn leaching and maintaining conductivity.
Implementation Method 1
natural or artificial graphite (graphite carbon materials) into/from which Li ions can be intercalated/deintercalated have been used for negative electrode materials
Implementation Method 2
charging/discharging can be performed smoothly because Si reactive with Li is in the form of ultrafine particles
Data Source
AI summary
The present invention provides a nonaqueous secondary battery with a high capacity, an excellent level of safety, and excellent charge-discharge cycle characteristics. The negative electrode contains, as negative electrode active materials, a graphite carbon material and a material containing Si as a constituent element, and the positive electrode includes, as a positive electrode active material, a lithium-containing composite oxide represented by the following general composition formula (1) and containing sulfur in a range of 0.01 mass % to 0.5 mass %:Li1+yMO2 (1)where y satisfies −0.3≦y<0.3, M represents a group of five or more elements including Ni, Co, Mn, Mg and at least one of Al, Ba, Sr, Ti and Zr, and when a, b, c and d represent Ni, Co, Mn, and Mg, respectively, in mol % and e represents a total of Al, Ba, Sr, Ti and Zr in mol % of all of the elements making up M, a, b, c, d, and e satisfy 70≦a≦97, 0.5<b<30, 0.5<c<30, 0.5<d<30, −10<c−d<10, −8≦(c−d)/d≦8, and e<10.