Silicon-Carbon Composite Anode With CMC/SBR for Cycle Stability
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Solution Overview
Problem
Silicon anodes for lithium-ion batteries face significant challenges due to high volume changes during lithiation and delithiation, leading to degradation, cracking, and poor cycle life, which limits their cycle stability and discharge capacity.
Innovation Solution
A silicon-carbon composite anode is developed, comprising 40-80 weight % silicon particles, 10-45 weight % carbon (carbon black and graphite), and a combination of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as binders, with specific ratios and processing methods to enhance mechanical stability and adhesion, using an aqueous solvent system to improve cycle stability and discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon anode material is used to increase theoretical capacity, then discharge capacity is improved, but volume change during lithiation and delithiation causes degradation and cracking leading to poor cycle life
Solution Approach 1:
The patent applies a flexible carbon coating shell around silicon particles to accommodate volume changes during lithiation and delithiation. This carbon layer acts as a flexible container that maintains structural integrity while allowing the silicon core to expand and contract, preventing cracking and degradation that would otherwise occur with rigid structures.
Solution Approach 2:
The patent creates a composite anode structure combining silicon particles with carbon materials (graphite, carbon black). The silicon provides high theoretical capacity while the carbon matrix provides structural stability and electrical conductivity. This composite approach allows the system to achieve >1000 mAh/gSi discharge capacity while maintaining good cycle life through the synergistic properties of both materials.
2Quantity of substance
If silicon anode material is used to increase theoretical capacity, then discharge capacity is improved, but mechanical stability deteriorates due to large volume changes
Solution Approach 1:
A flexible carbon coating is applied around silicon particles to provide mechanical stability. This carbon shell acts as a protective layer that maintains structural integrity during the 400% volume changes associated with silicon lithiation and delithiation, preventing particle fragmentation while allowing the necessary expansion and contraction.
Solution Approach 2:
The patent employs a composite structure where silicon particles are embedded in a carbon matrix containing graphite and carbon black. This composite material combines the high capacity of silicon with the mechanical stability and flexibility of carbon, achieving both improved discharge capacity and maintained structural integrity throughout cycling.
3Ease of manufacture
If conventional binders for carbon anodes are used for silicon anodes, then manufacturing process is simplified, but adhesion and binding strength are insufficient due to different binder requirements
Solution Approach 1:
The patent modifies binder parameters by selecting polymers with appropriate glass transition temperatures and chemical properties suitable for silicon anodes. Specifically, it uses SBR with Tg between -50°C to 0°C and CMC with specific molecular weights, which provide the necessary flexibility and adhesion for silicon's large volume changes, unlike conventional carbon anode binders.
Solution Approach 2:
The patent employs a composite binder system combining styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in specific ratios. This composite binder provides both the mechanical flexibility needed for silicon's volume expansion and the chemical adhesion required for strong binding, overcoming the limitations of single-component binders used in conventional carbon anodes.
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 silicon-carbon composite anode achieves over 1200 cycles with a cycling capacity of 600 mAh/gtot or 1000 mAh/gSi, significantly surpassing the theoretical capacity of graphite anodes, with improved mechanical stability and flexibility, and the use of fluoroethylene carbonate as an electrolyte additive further enhances the battery's performance.
Implementation Method 1
Charging and discharging processes are performed while lithium ions of a cathode are repeatedly intercalated into and de-intercalated from an anode
Implementation Method 2
a combination of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as binders
Data Source
AI summary
The present invention describes a silicon-carbon composite anode tor lithium-ion batteries comprising 40-80 weight % of silicon particles, 10-45 weight % of carbon, consisting of carbon black and graphite, and a combination of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SB.R) as a binder. The invention also comprises a method of manufacturing the anode and a Li-ion battery comprising the Si—C composite anode according to the present invention.