Lithium Secondary Battery Electrolyte for Stable SEI and CEI
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Solution Overview
Problem
Lithium secondary batteries face challenges in maintaining high energy density while improving cycling performance, kinetic performance, and storage life due to issues such as Li/Ni mixing, H2-H3 phase transition, and side reactions at the electrode interfaces, which affect cycle life and storage life.
Innovation Solution
Incorporating a positive electrode active material doped with elements like aluminum, zirconium, boron, magnesium, zinc, or titanium, and an electrolyte solution with C2-C8 alkenyl silane-based additives and lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide, or lithium tetrafluoroborate, to form stable SEI and CEI membranes, inhibiting doping element dissolution and reducing gas production reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the positive electrode active material is doped with elements like aluminum, zirconium, boron, magnesium, zinc, or titanium to improve energy density, then the energy density increases, but the structural stability during charging and discharging deteriorates due to Li/Ni mixing and H2-H3 phase transition
Solution Approach 1:
The patent applies local quality by doping specific elements (Al, Zr, B, Mg, Zn, Ti) at controlled concentrations (0.01-5 mol%) into the positive electrode active material lattice at specific sites. This creates local structural modifications that prevent Li/Ni mixing and stabilize the H2-H3 phase transition, thereby maintaining structural stability while preserving high energy density characteristics of the nickel-rich cathode material.
Solution Approach 2:
The patent employs composite materials by combining nickel-rich cathode material with multiple doping elements to create a composite structure. This composite approach allows the base material to provide high energy density while the dopant elements provide structural stabilization, resolving the contradiction between energy density and structural stability through material composition optimization.
2Reliability
If conventional electrolyte additives are used to form SEI membrane, then the SEI membrane forms, but the strength and toughness of the SEI membrane are insufficient, leading to repeated destruction and formation during cycling
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the electrolyte additive system. Specifically, it uses fluorinated cyclic carbonate additives (0.5-5 wt%) combined with chain carbonate additives (1-10 wt%) to change the chemical properties of the SEI membrane formed, resulting in enhanced strength and toughness that prevents repeated destruction during battery cycling.
Solution Approach 2:
The patent introduces fluorinated cyclic carbonate compounds as intermediary substances that mediate between the electrolyte and the electrode surface. These intermediaries preferentially react to form a stable, tough SEI membrane that protects the electrode from further degradation, thereby improving cycling performance through the intermediary's protective function.
3Use of energy by moving object
If the battery operates at high voltage to maintain high energy density, then the operating voltage remains high, but side reactions occur at the electrode interfaces including redox reactions of additives and dissolution of doping elements
Solution Approach 1:
The patent applies preliminary anti-action by using fluorinated cyclic carbonate additives that preferentially react with the electrode surface and electrolyte components before harmful side reactions can occur. This preliminary reaction forms a protective interface layer that prevents subsequent harmful redox reactions of conventional additives and dissolution of doping elements, allowing high voltage operation without the associated side reactions.
Solution Approach 2:
The patent converts the potentially harmful high voltage conditions into beneficial effects by using fluorinated cyclic carbonate additives that stabilize the electrode-electrolyte interface. The high voltage operation, which would normally cause harmful side reactions, instead promotes the formation of a stable protective interface through the fluorinated additive, transforming the harmful condition into a beneficial protective mechanism.
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
Enhances the stability and toughness of the SEI and CEI membranes, improving cycling and kinetic performance and prolonging the storage life of lithium secondary batteries by preventing membrane destruction and reducing side reactions.
Implementation Method 1
When the lithium secondary battery is formed, such a first additive participates in the membrane formation reaction of an SEI membrane (Solid Electrolyte Interface Membrane) on one side of a negative electrode plate
Implementation Method 2
Such a second additive can participate in and promote the formation of a CEI membrane on one side of a positive electrode plate to inhibit the dissolution of doping elements in a positive electrode active material
Implementation Method 3
inhibit the dissolution of doping elements in a positive electrode active material, thereby improving the structural stability of the positive electrode active material
Implementation Method 4
by promoting the formation of the CEI membrane, the second additive can effectively inhibit the redox reaction of the first additive on one side of the positive electrode plate, thereby avoiding or reducing the gas production effect
Data Source
Figure 1~3
Figure 4~6
AI summary
The present application discloses a lithium secondary battery and an electrical apparatus. The lithium secondary battery includes a positive electrode plate and an electrolyte solution, where the positive electrode plate includes a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material includes at least one doping element selected from aluminum, zirconium, boron, magnesium, zinc, calcium and titanium; the electrolyte solution includes a silane-based first additive containing C2-C8 alkenyl and a second additive, and the second additive is selected from at least one of lithium fluorosulfonate, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate; and the ratio of the mass percentage content W1 of the first additive in the electrolyte solution to the mass percentage content W2 of the second additive in the electrolyte solution to the mass percentage content W3 of the doping element in the positive electrode active material satisfies 1:(0.2-2):(0.1-0.5). The lithium secondary battery of the present application has good cycling performance, kinetic performance and storage life.