Malonic Silyl Ester Additives for High-Voltage Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries operating at high-voltage conditions face issues such as capacity loss and impedance rise due to irreversible lithium loss in the solid electrolyte interphase and resistive surface films, which are not effectively addressed by existing electrolyte additives.
Innovation Solution
The use of malonic silyl ester additives in lithium-ion batteries, which react with HF by-products to suppress transition metal dissolution and form a stable surface film at the cathode electrode, mitigating electrolyte oxidation and impedance issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common electrolyte additives such as vinylene carbonate (VC) and lithium bis(oxalate)borate (LiBOB) are used to provide a more robust solid-electrolyte interphase (SEI), then the protective effect on electrodes is improved, but the impedance of the cell is significantly increased due to the resistive nature of these surface films
Solution Approach 1:
The patent modifies the chemical structure of malonate-based additives by introducing silyl groups with specific substituents (R1, X, R2, R3) to change the properties of the formed surface film. This structural parameter change allows the film to provide protection while maintaining lower resistance compared to conventional additives like VC and LiBOB
Solution Approach 2:
The invention creates a composite surface film on electrodes through the action of multifunctional malonate silyl ester additives that combine multiple protective functions. The additive structure incorporates elements that simultaneously provide SEI formation, HF scavenging, and surface protection, resulting in a composite film with optimized properties balancing protection and conductivity
2Quantity of substance
If nickel-rich layered oxide materials are operated at high voltage (up to 4.5 V) to achieve high energy density, then capacity and power are improved, but electrolyte oxidation and transition metal dissolution occur due to repeated cycling at this operating voltage
Solution Approach 1:
The malonate silyl ester additives perform preliminary protective actions by forming stable surface films on the nickel-rich cathode before electrolyte oxidation and metal dissolution can occur. The additives preemptively scavenge HF and create protective layers that prevent the harmful reactions that would otherwise happen during high-voltage cycling
Solution Approach 2:
The multifunctional additives act as intermediaries between the high-voltage nickel-rich cathode and the electrolyte. They form interfacial layers that mediate the interaction, allowing high-voltage operation while preventing direct contact between the electrolyte and cathode surface that would cause oxidation and metal dissolution
3Adaptability or versatility
If trifunctional electrolyte additives are designed to react with HF, form protective films, and prevent electrolyte oxidation simultaneously, then multifunctionality is improved, but the complexity of additive design and synthesis is increased
Solution Approach 1:
The patent designs malonate silyl ester molecules with universal multifunctionality, where a single additive structure performs multiple functions: HF scavenging through silyl group reaction, SEI formation through malonate decomposition, and surface protection through film formation. This universal design allows one additive to replace multiple specialized additives
Solution Approach 2:
The invention merges multiple protective functions into a single additive molecule by combining malonate core structure with silyl ester groups. This merging of functions (HF scavenging, SEI formation, surface protection) into one compound simplifies the overall electrolyte formulation while maintaining comprehensive protection
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 malonic silyl ester additives enhance capacity retention and reduce impedance rise, maintaining high discharge capacity and power performance over cycles, effectively addressing the limitations of existing additives at high-voltage operations.
Implementation Method 1
The silyl ester groups can react with by-product HF formed during charge/discharge to suppress transition metal dissolution from the cathode electrode
Implementation Method 2
the core malonic ester moiety can form a stable surface film at the surface of the cathode electrode to prevent electrolyte oxidation
Data Source
AI summary
A non-aqueous electrolyte for a lithium-ion battery comprises a lithium salt and an additive in an organic solvent. The additive comprises a di-substituted malonate silyl ester compound, in which the hydrogens of the malonate methylene group are replaced by substituents R1 (e.g., alkyl) and X (e.g., halogen). Each of the carboxylic acid groups of the malonate are esterified by a monovalent silyl group such as —Si(R4)3; or the two carboxylic acid groups are esterified by a single divalent silylene group such as —Si(R5)2— to form a ring therewith. Each R4 and R5 independently is alkyl, phenyl, or alkoxy; and each substituted-alkyl comprises an alkyl moiety substituted with one or more group selected from alkenyl, alkynyl, hydroxy, halogen, alkoxy, carboxylic acid, carboxylic ester, carboxylic amide, phenyl, sulfonic acid, and phosphonic acid.