Graphite-Si/C Anode Electrolyte Balance for Stable SEI Batteries
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Solution Overview
Problem
Lithium secondary batteries using carbon-based negative electrode active materials face limitations in achieving high capacity and quick charging due to low reaction rates, while silicon-based materials suffer from volume changes causing SEI layer deterioration and electrolyte depletion, leading to reduced lifespan and durability.
Innovation Solution
A lithium secondary battery design incorporating a negative electrode active material layer composed of a graphite and Si/C composite, with a specific weight ratio, and an electrolyte containing non-fluorinated saturated cyclic carbonate and a fluorine-based compound, forms a stable SEI layer, inhibiting volume expansion and electrolyte side reactions, thereby enhancing capacity, lifespan, and high-temperature performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If carbon-based negative electrode active materials are used, then the battery structure is simple and manufacturing is easy, but the capacity is low and charging rate is slow
Solution Approach 1:
The patent uses a composite negative electrode active material consisting of silicon oxide particles (SiOx, 0≤x<1) coated with a carbon layer and further coated with a lithium phosphate layer. This composite structure combines the high capacity of silicon oxide with the structural stability and conductivity of carbon, achieving both high capacity and manufacturability
Solution Approach 2:
The patent applies a carbon coating layer beforehand on the silicon oxide particles to cushion the volume expansion during lithiation. The carbon layer acts as a buffer that accommodates the expansion stress, preventing particle breakage and maintaining structural integrity during charge-discharge cycles
2Quantity of substance
If silicon-based negative electrode active materials are used, then the capacity is high, but the volume changes cause SEI layer deterioration and electrolyte depletion
Solution Approach 1:
The patent applies a carbon coating layer beforehand on the silicon oxide particles to cushion the volume expansion during lithiation. The carbon layer acts as a buffer that accommodates the expansion stress, preventing particle breakage and maintaining structural integrity during charge-discharge cycles
Solution Approach 2:
The patent introduces a lithium phosphate coating layer as an intermediary between the silicon oxide core and the electrolyte. This intermediate layer mediates the interaction by providing a stable interface that prevents direct contact between the reactive silicon oxide and the electrolyte, thereby preventing SEI layer deterioration and electrolyte depletion
Solution Approach 3:
The patent uses a composite negative electrode active material consisting of silicon oxide particles (SiOx, 0≤x<1) coated with a carbon layer and further coated with a lithium phosphate layer. This composite structure combines the high capacity of silicon oxide with the structural stability and conductivity of carbon, achieving both high capacity and manufacturability
3Quantity of substance
If silicon-based negative electrode active materials are used, then the capacity is high, but the SEI layer deteriorates and electrolyte is depleted
Solution Approach 1:
The patent introduces a lithium phosphate coating layer as an intermediary between the silicon oxide core and the electrolyte. This intermediate layer mediates the interaction by providing a stable interface that prevents direct contact between the reactive silicon oxide and the electrolyte, thereby preventing SEI layer deterioration and electrolyte depletion
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 exhibits improved capacity characteristics, extended lifespan, and superior high-temperature stability by stabilizing the SEI layer and reducing resistance, even under significant volume changes, thus outperforming conventional designs.
Implementation Method 1
the electrolyte includes a non-fluorinated saturated cyclic carbonate and a fluorine-based compound in a weight ratio of 40:1 to 40:20, and the fluorine-based compound is present in an amount of 1 wt % to 5 wt % with respect to a total weight of the electrolyte
Data Source
AI summary
A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, an electrolyte, and a battery case accommodating the electrode assembly and the electrolyte. The negative electrode includes a negative electrode active material layer containing graphite and a Si/C composite. The positive electrode includes a positive electrode active material layer containing a lithium transition metal oxide represented by Formula 1. The graphite and the Si/C composite are present in a weight ratio of 93.1:6.9 to 99.9:0.1 in the negative electrode active material layer. The electrolyte includes a non-fluorinated saturated cyclic carbonate and a fluorine-based compound in a weight ratio of 40:1 to 40:20, and the fluorine-based compound is present in an amount of 1 wt % to 5 wt % with respect to a total weight of the electrolyte.Li1+x1[Niy1Coz1Mnw1M1v1]O2 [Formula 1]wherein all the variables in Formula 1 are described herein.