Rotaxane Polymer Binder for Silicon Anode Stability
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Solution Overview
Problem
Current polymer binders used in lithium secondary batteries, such as PVDF or SBR/CMC, are susceptible to volume changes during charging and discharging, leading to instability and poor adhesion in silicon negative electrode materials, limiting their application in medium- to large-sized batteries for electric vehicles.
Innovation Solution
A rotaxane polymer binder is developed, which includes a polymer based on a rotaxane structure, potentially cross-linked with polar or nonpolar polymers, and is used in conjunction with active materials like silicon, tin, or metal oxides, to maintain electrode stability and adhesion through supramolecular structures that distribute stress effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymer binders (PVDF or SBR/CMC) are used in silicon negative electrode materials, then the electrode can be assembled and function initially, but the binder becomes susceptible to volume change during charging and discharging, leading to delamination and interfacial instability
Solution Approach 1:
The patent changes the chemical and physical parameters of the binder by introducing a rotaxane molecular structure with moving crosslinks. This dynamic structure allows the binder to adapt its properties during volume changes, maintaining both mechanical integrity and adhesion stability throughout charge-discharge cycles.
Solution Approach 2:
The rotaxane binder incorporates dynamic moving crosslinks that can relocate within the polymer matrix in response to volume expansion and contraction. This dynamic behavior enables the binder to maintain continuous contact with silicon particles while accommodating structural changes, preventing delamination and interfacial instability.
2Quantity of substance
If silicon negative electrode material is used to achieve high theoretical capacity (4200 mAh/g), then energy density is improved, but 300% volume expansion/contraction during charging and discharging causes micronization, delamination, and interfacial instability
Solution Approach 1:
The rotaxane binder acts as a flexible molecular network that envelops and accommodates silicon particles during volume changes. The moving crosslinks create a dynamic flexible structure that can expand and contract with the silicon, preventing structural degradation while maintaining electrode integrity.
Solution Approach 2:
The dynamic moving crosslinks in the rotaxane binder enable the electrode structure to adapt continuously to the 300% volume expansion and contraction of silicon. This dynamic response prevents micronization and delamination by maintaining mechanical connectivity throughout the charge-discharge cycles.
3Reliability
If a stable electrode structure is maintained despite repeated volume change, then reliability is improved, but conventional binders are susceptible to volume change and cannot maintain adhesion
Solution Approach 1:
The moving crosslinks in the rotaxane binder create a dynamic network that can relocate to maintain optimal adhesion strength during volume changes. This dynamic adjustment allows the binder to preserve both structural stability and adhesion strength simultaneously, overcoming the limitation of conventional static binders.
Solution Approach 2:
The rotaxane binder changes its physical parameters dynamically through the movement of crosslinks, adjusting its mechanical properties to match the volume changes of the electrode. This parameter adaptation enables the binder to maintain both structural stability and adhesion strength under varying conditions.
Data Source
AI summary
The present disclosure provides a rotaxane polymer binder containing a polymer based on a rotaxane structure. The polymer binder may further contain a polymer cross-linked with a polar polymer. The polar polymer may be a polymer containing the element F, O or N in a functional group and having high polarity.In addition, the present disclosure provides an electrode containing the rotaxane polymer binder as a binder for a lithium secondary battery, and a secondary battery containing the electrode.