Polyacrylic Acid Binder for Silicon Anode Cycle Life
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Solution Overview
Problem
Conventional binders used in lithium-ion rechargeable battery cells, such as PVDF and SBR, fail to effectively bind silicon particles together over successive charging cycles due to large volume changes, leading to loss of electrical contact and reduced cycle life, especially with lower-grade silicon that contains impurities.
Innovation Solution
Poly(acrylic acid) (PAA) is used as a binder, forming a cohesive mass with silicon that maintains electrical contact with the current collector and supports a substantial number of discharge/recharge cycles, even with lower purity silicon, by forming homo- or copolymers from specific monomers and their alkali metal salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional binders (PVDF, SBR) are used to bind silicon particles, then the electrode structure is maintained initially, but the binder fails over successive charging cycles due to large volume changes, leading to loss of electrical contact
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by using polyacrylic acid and its derivatives instead of conventional PVDF or SBR binders. This parameter change enables the binder to withstand the large volume changes (up to 300%) associated with silicon lithiation-delithiation cycles, thereby improving cycle life while maintaining stability.
Solution Approach 2:
The invention employs composite binder systems combining polyacrylic acid with other materials such as carboxymethyl cellulose or conductive polymers. This composite approach creates a synergistic effect where the polyacrylic acid provides robust binding during volume changes while the complementary materials enhance conductivity or structural integrity, resolving the contradiction between reliability and stability.
2Quantity of substance
If lower-grade silicon with impurities is used to increase capacity, then energy density improves, but binder stability deteriorates due to chemical incompatibility with impurities
Solution Approach 1:
The invention changes the chemical parameters of the binder system to be more tolerant of impurities. Polyacrylic acid and its derivatives exhibit greater chemical stability and compatibility with common silicon impurities compared to conventional binders, enabling the use of lower-grade, higher-capacity silicon without sacrificing reliability.
Solution Approach 2:
The invention accepts the use of lower-cost, lower-purity silicon materials that would otherwise be incompatible with conventional binders. By using a more robust binder system, the invention effectively treats the silicon active material as a disposable, high-capacity component that can be optimized for performance rather than purity, improving energy density while maintaining reliability.
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
PAA binders provide stable cycle life performance and overcome the instability issues of NaCMC with impurities, enabling effective binding of silicon particles across various grades, maintaining electrical contact and extending the battery's capacity to hold a charge.
Implementation Method 1
a polymeric binder, characterised in that the polymeric binder is a homo-polymer or copolymer of one or more monomers selected from the group consisting acrylic acid, 3-butenoic acid, 2-methacrylic acid, 2-pentenoic acid, 2,3-dimethylacrylic acid, 3,3-dimethylacrylic acid, trans-butenedioc acid, cis-butenedioc acid and itaconic acid
Data Source
AI summary
An electrode for lithium ion recharged battery cell includes current collectors, a cathode layer, a separator and a cohesive anode mass. The cohesive anode mass includes silicon as an active material and a polymeric binder. The polymeric binder is a homo-polymer or copolymer of one or more monomers selected from the group consisting of acrylic acid, 3-butenoic acid, 2-methacrylic acid, 2-pentenoic acid, 2,3-dimethylacrylic acid, 3,3-dymethylacrylic acid, trans-butenedioc acid, cis-butenedioc acid and itaconic acid and optionally an alkali metal salt thereof. The silicon can include 20 to 100% of the active material in the cohesive mass. The binder is mixed with the silicon to form the cohesive mass that adheres to the current collector and maintains the cohesive mass in electrical contact with the current collector.