Battery Electrolytes Including Solvents Comprising Cyclic Acetals

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This invention covers a new class of electrolyte solvents for rechargeable batteries, based on cyclic acetals — ring-shaped organic molecules derived from sugar alcohols (such as erythritol, xylitol, or sorbitol) reacted with aldehydes or ketones. These solvents can be used alone or mixed with water as a co-solvent in battery electrolytes, and they enable a dramatically lower concentration of conducting salt compared to conventional formulations. A key example is (3aR,6aS)-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol (THFD), which shows an electrochemical stability window up to 5.2 V and an unusually high lithium-ion transference number of ~0.5. The solvents are synthesizable in a single step from renewable feedstocks, making the electrolyte both high-performing and sustainable.

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• Lithium-ion batteries for electric vehicles, where the wide electrochemical stability window (up to 5.2 V) enables use with high-voltage cathode materials.
• Aqueous rechargeable batteries (e.g., lithium-manganese oxide against activated carbon) where the cyclic acetal acts as a diluent to extend the stability window of water-based electrolytes while reducing salt loading by a factor of 10.
• Sodium-ion and zinc-ion batteries requiring tailored electrolytes with good ionic conductivity and electrochemical stability.
• Stationary energy storage systems where lower electrolyte cost and improved safety (reduced flammability via water co-solvent) are priorities.
• Battery research and development applications requiring electrolytes synthesized from bio-based, renewable raw materials for sustainability assessments.
• Low-temperature battery applications, as the cyclic acetal/water electrolyte shows only a glass transition at −90 °C rather than crystallization at −10 °C seen in conventional water-in-salt electrolytes.

BenefitsContent extracted from patent full text and abstract with AI.

• The conducting salt concentration can be reduced by up to 10-fold (e.g., from 21 mol/kg to 2.1 mol/kg) compared to conventional water-in-salt electrolytes, lowering material cost and environmental impact.
• The cyclic acetal solvents achieve a lithium-ion transference number of approximately 0.5, significantly higher than the 0.2–0.4 typical of standard liquid electrolytes, improving effective lithium transport.
• An electrochemical stability window of up to 5.2 V vs. Li⁺/Li is demonstrated, enabling compatibility with high-voltage electrode materials.
• The solvents are produced in a single synthetic step from bio-based, renewable sugar alcohols, making them more sustainable and potentially lower-cost than fluorinated or petroleum-derived alternatives.
• When used as a co-solvent with water, the cyclic acetal lowers the freezing/crystallization point of the electrolyte to below −90 °C, broadening the operational temperature range.
• Galvanostatic cycling tests show stable capacity retention and higher Coulombic efficiency compared to the 21 mol/kg LiTFSI reference electrolyte, despite the much lower salt concentration.

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Patent Abstract

[0001] The present invention relates to a solvent-based electrolyte for an electrochemical energy storage device, comprising at least the following constituents: - at least one solvent; and - at least one conducting salt, wherein at least one solvent corresponds to the following formula (1): <img class="EMIRef" id="0b041c72-4da7-462f-902d-2476896723ae-ia01" /> wherein - R and R<1> are the same or different and are selected from the group consisting of H, CH<3>, the structure according to formula (3) and the structure according to formula (4), or R and R<1> together form the structure according to formula (2), wherein - formula (2) corresponds to the following structure: <img class="EMIRef" id="0b041c72-4da7-462f-902d-2476896723ae-ia02" /> - formula (3) corresponds to the following structure: <img class="EMIRef" id="0b041c72-4da7-462f-902d-2476896723ae-ia03" /> wherein n is an integer from 1 to 10; - formula (4) corresponds to the following structure: wherein in formulas (1), (3), and (4) R<2> and R<3> are the same or different and are selected from the group consisting of H, (CH<2>)<x>-CH<3>, wherein x is an integer from 0 to 9.