Pre-Lithiated Li-Ion Battery Electrolyte for Long Cycle Life
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Solution Overview
Problem
Lithium-ion batteries face challenges in achieving long cycle life and high energy density due to capacity loss from side reactions at the negative electrode, particularly with the formation of a solid electrolyte interface (SEI) film, which limits their application in long-life electric buses and large-scale energy storage systems.
Innovation Solution
A lithium-ion battery design incorporating a cyclic ester organic solvent in the electrolyte, with a mass ratio of cyclic ester to total organic solvent of ≤10%, and a pre-lithium-intercalation compound (LiCx) negative electrode active material, ensuring stable film formation and sufficient lithium ion vacancies, along with a balanced capacity ratio between the negative and positive electrode active materials to prolong cycle and storage life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a lithium-ion battery uses graphite as a negative electrode active material, then the energy density is improved, but the cycle life deteriorates due to continuous SEI film formation and active lithium ion loss
Solution Approach 1:
The patent applies preliminary action by pre-lithiating the graphite negative electrode material before battery assembly. This is achieved by contacting the graphite with lithium metal or lithium-containing compounds during the electrode manufacturing process, creating a pre-formed SEI layer and introducing excess lithium ions. This preliminary lithiation ensures that the SEI film is formed with sufficient lithium ions before the battery enters service, preventing continuous lithium ion consumption and extending cycle life while maintaining high energy density.
Solution Approach 2:
The patent changes the lithium ion concentration parameter in the negative electrode by controlling the lithiation degree of graphite. By adjusting the amount of lithium metal or lithium-containing compounds added during electrode preparation, the patent optimizes the initial lithium ion content in the SEI film and the graphite structure. This parameter change allows the battery to achieve both high energy density and extended cycle life by balancing the lithium ion availability for SEI formation and capacity delivery.
2Stability of the object's composition
If the amount of cyclic ester in the electrolyte is increased, then the film formation stability is improved, but the lithium ion transmission rate deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of cyclic ester in the electrolyte to a specific range (5-30% by volume). This parameter optimization balances the competing requirements: sufficient cyclic ester to form stable SEI films on the graphite surface, but not so much as to excessively increase electrolyte viscosity and hinder lithium ion diffusion. The patent also adjusts the ratio of cyclic carbonate to chain carbonate components to achieve optimal film stability and ion transmission.
Solution Approach 2:
The patent uses a composite electrolyte system combining multiple components: cyclic esters (EC, PC), chain carbonates (DMC, DEC, EMC), and lithium salts. This composite electrolyte formulation leverages the complementary properties of each component - cyclic esters provide stable SEI formation, chain carbonates ensure good ion conductivity and low viscosity, and lithium salts provide ionic conductivity. The synergistic combination resolves the contradiction between film stability and ion transmission rate.
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 battery achieves extended cycle life of 10000 or more times, meeting the requirements for long-life electric buses and large-scale energy storage systems by stabilizing the negative electrode and optimizing lithium ion transmission rates, thereby reducing capacity loss and enhancing overall battery performance.
Implementation Method 1
the carbon-based negative electrode material in the negative electrode film exists in a form of a pre-lithium-intercalation compound LiC x formed by lithiation with a lithium metal
Implementation Method 2
the organic solvent in the electrolyte comprises a cyclic ester, and a mass of the cyclic ester is equal to or less than 10% of a total mass of the organic solvent in the electrolyte
Data Source
Figure 1
AI summary
The present invention provides a lithium-ion battery comprising an electrode assembly, an electrolyte and a case. The electrolyte comprises a lithium salt and an organic solvent which comprises a cyclic ester, a mass of the cyclic ester is equal to or less than 10% of a total mass of the organic solvent. A negative electrode active material at least comprises a carbon-based negative electrode material which in the negative electrode film exists in a form of a pre-lithium-intercalation compound LiCx formed by lithiation with a lithium metal, 12≤x≤150; a capacity of the negative electrode active material per unit area / (a capacity of the positive electrode active material per unit area + a capacity of active lithium ions of the pre-lithium-intercalation compound LiCx which can be intercalated and deintercalated in the negative electrode film per unit area) ≥ 1.10.