Si/SiOx Core Electrode with Carbon Coating for Cycle Life
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Solution Overview
Problem
Current electrode active materials for lithium secondary batteries face challenges in achieving high charge/discharge capacity and cycle life characteristics, with silicon-carbon composite materials exhibiting low charge/discharge efficiency and poor cycle life, while oxide materials show high irreversible capacity and low discharge capacity.
Innovation Solution
An electrode active material comprising a core layer of metal or metalloid with a metal oxide, coated with an amorphous carbon layer and a crystalline carbon layer, which inhibits volume variations during charge/discharge cycles and maintains high electric conductivity, is developed. The method involves mixing metals or metalloids with metal oxides and crystalline carbon, followed by mechanical alloying or thin film vapor deposition to form the amorphous and crystalline carbon layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-carbon composite materials are used as electrode active materials, then high discharge capacity is achieved, but charge/discharge efficiency and cycle life characteristics deteriorate
Solution Approach 1:
The patent uses a composite structure consisting of a core layer containing Si/SiOx and an outer amorphous carbon layer. This composite design combines the high capacity benefits of silicon with the stability and conductivity of carbon, resolving the contradiction between achieving high discharge capacity and maintaining good cycle life characteristics. The amorphous carbon layer acts as a protective matrix that accommodates silicon volume changes while maintaining structural integrity over multiple cycles.
Solution Approach 2:
The amorphous carbon layer functions as a flexible protective shell surrounding the Si/SiOx core. This thin film structure accommodates the volume expansion and contraction of silicon during lithiation and delithiation cycles, preventing structural degradation and maintaining charge/discharge efficiency over extended cycling, thus improving cycle life characteristics.
2Reliability
If oxide materials including SiOx or SnOx are used as electrode active materials, then charge/discharge efficiency is improved, but discharge capacity decreases and irreversible capacity increases
Solution Approach 1:
The patent merges two materials with complementary properties: Si (providing high discharge capacity) and SiOx (providing high charge/discharge efficiency). The core layer contains both Si and SiOx in specific ratios, allowing the electrode to achieve both high capacity and high efficiency by combining the advantageous properties of each material.
Solution Approach 2:
The patent optimizes the ratio of Si to SiOx in the core layer and controls the thickness of the amorphous carbon layer to achieve the desired balance between discharge capacity and charge/discharge efficiency. By adjusting these parameters, the electrode can be tuned to meet specific performance requirements.
3Reliability
If carbonaceous materials are mixed with oxide materials in composite materials, then problems of pure oxide materials are partially solved, but capacity drops
Solution Approach 1:
The patent uses a thin amorphous carbon layer as a protective shell rather than mixing carbonaceous materials throughout the composite. This thin film approach provides the necessary structural support and conductivity without significantly increasing the mass of non-active carbon, thus avoiding the capacity drop associated with carbon mixtures while still improving cycle life.
Solution Approach 2:
The carbon is concentrated in a thin outer layer rather than being distributed throughout the composite material. This local concentration of carbon provides the necessary protective and conductive functions at the interface where they are most needed, while minimizing the amount of carbon that does not participate in lithium storage reactions.
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 electrode active material achieves high charge/discharge capacity and improved cycle life characteristics by stabilizing volume variations and ensuring smooth lithium intercalation/deintercalation, maintaining efficiency and conductivity throughout repeated cycles.
Implementation Method 1
the electrode active material according to the present invention inhibits variations in volume of the core layer that may occur during charge/discharge cycles
Implementation Method 2
Such lithium secondary batteries produce electric energy via redox reactions upon the lithium ion intercalation/ deintercalation at the cathode and the anode
Implementation Method 3
The method involves mixing metals or metalloids with metal oxides and crystalline carbon, followed by mechanical alloying or thin film vapor deposition to form the amorphous and crystalline carbon layers
Implementation Method 4
The method involves mixing metals or metalloids with metal oxides and crystalline carbon, followed by mechanical alloying or thin film vapor deposition to form the amorphous and crystalline carbon layers
Implementation Method 5
maintains a high electric conductivity and conduction paths among electrode active material particles
Data Source
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AI summary
Disclosed is an electrode active material comprising: (a) a core layer containing (i) a metal and/or metalloid capable of repeating lithium intercalation/ deintercalation, and (ii) a metal oxide and/or metalloid oxide capable of repeating lithium intercalation/ deintercalation; (b) an amorphous carbon layer coated on a surface of the core layer; and (c) a crystalline carbon layer coated on the amorphous carbon layer. An electrochemical device comprising the electrode active material is also disclosed.