SiOx Anode Material with LiF Shell for Cycle-Stable Lithium Batteries
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Solution Overview
Problem
Lithium secondary batteries face challenges with silicon-based negative electrode active materials, which experience degradation and rapid volumetric expansion, leading to low initial efficiency and life characteristics, despite efforts to improve these aspects using silicon oxides and fluoroethylene carbonate additives.
Innovation Solution
A negative electrode active material comprising a silicon oxide core with a lithium silicate intermediate layer and a LiF coating layer, where the lithium silicate layer is present in 5-15 wt% and the LiF coating layer is 0.1-3 wt%, forming a nanocomposite structure that enhances initial efficiency and stability by minimizing structural collapse and electrolyte depletion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based materials are used as negative electrode active material, then capacity is improved, but life characteristics degrade and volumetric expansion occurs rapidly
Solution Approach 1:
The negative electrode active material is segmented into multiple functional layers: a silicon oxide core (0.5 < x ≤ 2 in SiOx) providing high capacity, an intermediate layer (5-15 wt%) buffering volumetric expansion, and an outer coating layer (0.1-3 wt% LiF) preventing electrolyte depletion. This segmentation allows each layer to perform its specific function while working together to achieve both high capacity and long cycle life.
Solution Approach 2:
The invention uses a composite material structure combining silicon oxide (for high capacity), intermediate layer material (for structural stability during expansion), and LiF coating (for electrolyte protection). This composite approach leverages the advantages of each material while mitigating their individual disadvantages, achieving both high capacity and improved reliability.
2Reliability
If silicon oxide is used to improve life characteristics and reduce volumetric expansion, then stability is improved, but initial efficiency decreases due to irreversible phase formation
Solution Approach 1:
The invention optimizes the compositional parameters of the silicon oxide core (using SiOx where 0.5 < x ≤ 2 rather than pure SiO2) and the ratios of each layer (intermediate layer 5-15 wt%, LiF coating 0.1-3 wt%). These parameter changes balance the trade-off between stability and initial efficiency, ensuring that the material forms a stable structure while maintaining good initial charge-discharge performance.
Solution Approach 2:
Different regions of the negative electrode active material have different compositions and functions: the silicon oxide core (0.5 < x ≤ 2) provides high capacity with controlled expansion, the intermediate layer (5-15 wt%) provides structural buffer, and the outer LiF coating (0.1-3 wt%) provides electrolyte protection. This local quality differentiation allows each region to optimize its specific function while contributing to overall performance.
3Reliability
If fluoroethylene carbonate is used as electrolyte additive to improve life characteristics, then stability is improved, but cost increases and gas generation occurs during high temperature storage
Solution Approach 1:
The invention extracts and eliminates the need for fluoroethylene carbonate electrolyte additive by incorporating LiF coating directly onto the negative electrode active material surface. This alternative approach achieves the same protective function (improving life characteristics) without the harmful side effects (gas generation during high temperature storage) and reduces cost.
Solution Approach 2:
The LiF coating layer acts as an intermediary between the silicon oxide core and the electrolyte, providing protection against electrolyte depletion and improving life characteristics without requiring fluoroethylene carbonate additive. This intermediary layer prevents direct harmful interactions while maintaining stable performance.
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 proposed structure improves initial efficiency and life characteristics by forming a stable solid electrolyte interface, reducing volumetric expansion, and maintaining discharge capacity, outperforming batteries without the LiF coating layer.
Implementation Method 1
it causes degradation of life characteristics during repeated charge/discharge and shows rapid volumetric expansion. Thus, some studies have been conducted to improve life characteristics and to alleviate volumetric expansion by using silicon oxides (SiO x ).
Implementation Method 2
The negative electrode active material according to an embodiment of the present disclosure improves initial efficiency and life characteristics by forming a stable solid electrolyte interface
Implementation Method 3
the lithium silicate-containing layer may have a thickness of 1-1,000 nm, 10-800 nm, or 100-500 nm
Data Source
AI summary
The present disclosure relates to a negative electrode active material including a core, an intermediate layer and a shell layer, wherein the core includes a silicon oxide of SiOx (0 < x < 2); the intermediate layer is a lithium silicate-containing layer disposed on the surface of the silicon oxide; the shell layer is a LiF coating layer disposed on the surface of the silicate-containing layer; and the lithium silicate-containing layer is present in an amount of 5-15 wt% based on the total weight of the negative electrode active material. The present disclosure also relates to a method for preparing the negative electrode active material, and a negative electrode and lithium secondary battery including the same. The negative electrode active material provides excellent initial efficiency and life characteristics.