CsDFP Negative Electrode Slurry for Stable SEI and Dendrite Suppression
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Solution Overview
Problem
Lithium secondary batteries face issues with lithium dendrite formation during high-rate charging, leading to internal short circuits and potential fires due to the limited lithium ion conductivity of graphite and the instability of existing electrolyte additives like CsF6P and LiPO2F2, which are easily soluble and consumed during cycling, failing to effectively inhibit dendrite growth.
Innovation Solution
A preparation method for cesium difluorophosphate (CsDFP) is used in the negative electrode slurry, allowing for continuous formation of a solid electrolyte interface (SEI) film to repair and stabilize the SEI, reducing activation energy for lithium ion intercalation, and incorporating CsDFP into the electrode slurry and plate to enhance compatibility and slow release, thereby inhibiting dendrite growth and improving cycle life and high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If graphite materials are used as negative electrode active materials, then the battery structure is simple and manufacturing is easy, but lithium ion conductivity is limited causing lithium dendrite formation during high-rate charging
Solution Approach 1:
CsDFP acts as an intermediary substance between the lithium ions and graphite negative electrode. It forms a stable SEI film that mediates the interaction, allowing smooth lithium ion insertion/extraction without direct harmful contact between lithium ions and graphite structure, thereby preventing dendrite formation while maintaining good manufacturability
Solution Approach 2:
The invention changes the chemical composition parameter of the electrolyte by introducing CsDFP, which has specific molecular structure characteristics (difluorophosphate group) that alter the SEI film formation parameters. This parameter change leads to improved lithium ion conductivity and dendrite suppression while maintaining graphite as the negative electrode material
2Reliability
If cesium salts like CsF6P are added to the electrolyte to prevent lithium dendrites, then dendrite growth is inhibited, but the additive is easily soluble and consumed at one time in the formation stage, failing to provide long-term protection
Solution Approach 1:
CsDFP performs preliminary action by forming a stable SEI film during the formation stage that is designed to be durable and self-repairing. The additive预先 (in advance) creates a protective layer that withstands subsequent cycling, unlike conventional additives that are completely consumed in the first stage
Solution Approach 2:
CsDFP enables continuous useful action by maintaining its functionality throughout the battery's cycling life. The additive continuously repairs and maintains the SEI film integrity during charge-discharge cycles, providing ongoing protection against dendrite growth rather than a one-time effect
3Reliability
If lithium difluorophosphate (LiPO2F2) is added to the electrolyte to reduce DC impedance, then impedance is reduced, but the additive is still easily soluble and consumed, failing to prevent lithium dendrite growth in the long term
Solution Approach 1:
The invention changes the cation parameter from lithium (Li+) to cesium (Cs+), which fundamentally alters the solubility and stability parameters of the difluorophosphate additive. CsDFP exhibits different electrochemical behavior including lower solubility and higher stability, enabling long-term impedance reduction and dendrite suppression
Solution Approach 2:
CsDFP can be viewed as a composite functional material combining the benefits of cesium salts (low solubility, high stability) with difluorophosphate group (impedance reduction, SEI film formation). This composite structure achieves both low impedance and long-term durability
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
CsDFP in the negative electrode slurry reduces impedance growth, facilitates easier lithium ion intercalation, and forms stable SEI films, resulting in improved rate performance, high-temperature storage, and long-term cycle performance of secondary batteries.
Implementation Method 1
carrying out ion exchange reactions with LiPO2F2 and a cesium source to yield CsDFP
Implementation Method 2
films can be continuously formed to repair the solid electrolyte interface (SEI) film
Implementation Method 3
reduce the activation energy of lithium ions intercalated into the negative electrode (that is, it is easier for the intercalation and deintercalation of the lithium ions)
Data Source
AI summary
A preparation method of CsDFP for aqueous negative electrode slurry includes carrying out ion exchange reactions with LiPO2F2 and a cesium source. The activation energy of Li+ intercalation in the negative electrode is reduced due to the existence of Cs+, leading to a better rate performance. Further, the impedance growth rate of the batteries is reduced and the high temperature storage performance is excellent since PO2F2— participates in the electrochemical reaction to form a stable low-impedance SEI film on the surface of the negative electrode plate. Moreover, films are continuously formed to repair the SEI films under the gradual release of CsDFP, which is conducive to inhibiting the growth of lithium dendrites during long-term high-rate cycling, thereby obtaining an improved cycle performance.