Sodium Polyacrylate Binder for Silicon Anode Adhesion
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Solution Overview
Problem
Current composite electrode materials for lithium-ion batteries, particularly those using silicon-based anodes, face challenges such as significant volume changes during charging and discharging, leading to stress, cohesion loss, and adhesion issues with the current collector, which results in reduced cycle life and increased internal resistance.
Innovation Solution
A composite electrode material is developed using a sodium polyacrylate binder with a molecular weight of 300,000 to 3,000,000, where 40 to 90% of the carboxyl groups are in the form of metal ion carboxylate salts, providing improved adhesion, cohesion, and stability, and accommodating volume changes during battery cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based anode material is used to increase gravimetric capacity, then battery energy density is improved, but volume change during charging/discharging causes stress and adhesion loss
Solution Approach 1:
The patent modifies the binder's molecular weight parameter (300,000 to 3,000,000) and chemical composition (sodium polyacrylate with metal ion carboxylate salts) to create a binder that can accommodate silicon's volume expansion while maintaining adhesion. This parameter optimization allows the electrode to retain structural integrity despite the 300% volume change during lithium insertion.
Solution Approach 2:
The patent creates a composite binder system combining sodium polyacrylate with metal ion carboxylate salts (40-90% conversion). This composite material provides both the flexibility needed to accommodate volume changes and the adhesive strength to maintain bonding with the current collector during cycling.
2Quantity of substance
If silicon-based anode material is used to increase gravimetric capacity, then battery energy density is improved, but electrode material cracks and cohesion is lost
Solution Approach 1:
The patent optimizes the molecular weight parameter of the binder to 300,000-3,000,000, which provides the right balance between flexibility and strength. This molecular weight range enables the binder to stretch and accommodate silicon expansion without breaking, thereby maintaining cohesion throughout the electrode composite.
Solution Approach 2:
The sodium polyacrylate binder acts as an intermediary material between the silicon particles and the current collector. It absorbs the mechanical stress of volume expansion and distributes it throughout the composite, preventing crack formation and maintaining overall structural cohesion.
3Ease of manufacture
If conventional binder is used in silicon-based anodes, then manufacturing is simple, but adhesion and cohesion are insufficient during cycling
Solution Approach 1:
The patent specifies precise parameter ranges for the binder: molecular weight (300,000-3,000,000) and metal ion carboxylate salt content (40-90%). These optimized parameters ensure both ease of manufacture through solution casting and superior adhesion/cohesion performance during battery cycling.
Solution Approach 2:
The patent introduces local quality variation by converting 40-90% of carboxyl groups to metal ion carboxylate salts, creating regions of different chemical properties within the binder. This partial conversion optimizes the balance between adhesion (provided by ionic groups) and flexibility (provided by polyacrylate chains).
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 composite electrode material exhibits excellent capacity retention, with discharge capacities exceeding 500 mAh/g, and a cycle life of over 100 cycles, with cells maintaining 50% of their initial capacity after 100 cycles, and showing improved adhesion and cohesion properties.
Implementation Method 1
accommodating volume changes during battery cycles
Implementation Method 2
40 to 90% of the carboxyl groups are in the form of metal ion carboxylate salts
Implementation Method 3
lithium ions migrate from the lithium containing composite metal oxide layer of the cathode to the anode
Implementation Method 4
lithium ions migrate from the lithium containing composite metal oxide layer of the cathode to the anode where they become embedded in the graphite in a process known as insertion to form a lithium carbon insertion compound
Data Source
Figure 1a
Figure 1b~2
Figure 3~4
AI summary
The present invention relates to a composite electrode material for a rechargeable battery; to a method of making a composite electrode material; to an electrode comprising the composite electrode material, especially an anode; to cells including electrodes or anodes including the composite electrode material; and to devices including said cells. In particular, there is provided a composite electrode material for a rechargeable battery cell comprising: a. an electroactive material; and b. a polymeric binder including pendant carboxyl groups characterised in that (i) the electroactive material comprises one or more components selected from the group comprising an electroactive metal, an electroactive semi-metal, an electroactive ceramic material, an electroactive metalloid, an electroactive semi-conductor, an electroactive alloy of a metal, an electroactive alloy of a semi metal and an electroactive compound of a metal or a semi-metal, (ii) the polymeric binder has a molecular weight in the range 300,000 to 3,000,000 and (iii) 40 to 90% of the carboxyl groups of the polymeric binder are in the form of a metal ion carboxylate salt.