Iron Sodium Hydroxysulphide Anode Material for Swelling-Resistant Na-Ion Cells
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Solution Overview
Problem
Existing sodium-ion batteries face challenges with mechanical ageing and swelling due to the soft nature of sulphide-based negative electrode materials, which limit their performance and safety, and there is a lack of effective materials that can support high charging and discharge rates.
Innovation Solution
A compound of formula (NaOH)x[Fe(OH)2]yFeS is synthesized through a method involving equimolar mixing of iron and sodium sulphide in an NaOH aqueous solution, followed by heating and drying, which results in a lamellar structure promoting reversible sodium mobility and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulphide-based negative electrode materials are used, then good sodium ion mobility and electrical conductivity are achieved, but mechanical ageing and swelling occur due to the soft nature of these compounds
Solution Approach 1:
The invention uses a composite material consisting of iron sulphide combined with hydroxysulphide phases. This composite structure leverages the advantages of both components: iron sulphide provides good sodium ion mobility and electrical conductivity, while the hydroxysulphide component adds mechanical strength and structural stability, preventing swelling and mechanical ageing during sodium insertion/extraction cycles.
2Productivity
If transition metal sulphides with lamellar structures are used, then rapid sodium diffusion and high capacity are achieved, but mechanical deformation and swelling occur during insertion/de-insertion
Solution Approach 1:
The invention modifies the local quality of the lamellar structure by incorporating hydroxysulphide phases at specific locations within the structure. These localized modifications provide structural support at critical regions where deformation occurs during sodium insertion/extraction, maintaining the overall lamellar architecture's advantage for rapid ion diffusion while preventing excessive structural deformation.
3Reliability
If sulphide materials free of sodium are used, then good electrical conductivity is achieved, but additional sodium sources are required which complicates battery design
Solution Approach 1:
The iron sulphide hydroxysulphide compound serves multiple functions simultaneously: it provides good electrical conductivity like traditional sulphides, offers structural stability to prevent swelling, and contains built-in sodium content that eliminates the need for separate sodium sources. This multi-functionality simplifies battery design while maintaining 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 compound achieves high reversible capacity and good electrical conductivity, supporting high charging and discharge rates, with capacities up to 110 mAh/g and reduced mechanical deformation, enhancing battery performance and safety.
Implementation Method 1
the strong valence of the sulphides ensures a good mobility of the sodium ion... Many transition metal sulphides (MoS2, TiS2) have lamellar structures into lamellae between which the sodium can diffuse rapidly in large amounts
Implementation Method 2
the strong valence of the sulphides ensures a good mobility of the sodium ion and a good electron mobility (ensuring a good electrical conductivity)
Implementation Method 3
b. Heating the obtained mixture up to a temperature comprised between 110° C. and 210° C. for a duration comprised between 1 hour and one week
Implementation Method 4
Mixing iron and sodium sulphide in equimolar amounts, in an NaOH aqueous solution... Heating the obtained mixture
Data Source
AI summary
A process for preparing a compound of formula (NaOH)x[Fe(OH)2]yFeS, may include: (a) mixing iron and sodium sulfide in equimolar amounts, in an NaOH aqueous solution; (b) heating the obtained mixture up to a temperature in a range of from 110 to 210° C. for a duration in a range of from 1 hour to 1 week; and (c) recovering the active material by filtering and drying in a neutral atmosphere.