Amorphous Lithium Niobium Sulfide Cathode
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Solution Overview
Problem
Current lithium secondary batteries face limitations in achieving high charge-discharge capacity and electrical conductivity due to the structural constraints of crystalline titanium sulfides, which hinder the development of high-capacity cathodes, and existing solutions like sulfur-based materials suffer from low conductivity and polysulfide dissolution issues.
Innovation Solution
The development of amorphous (lithium) niobium sulfides and (lithium) titanium niobium sulfides with high sulfur content, produced through mechanical milling of niobium, titanium, sulfur, and lithium sources, which exhibit enhanced charge-discharge capacity and conductivity by creating a matrix with crystalline metal sulfides or carbon, allowing for increased lithium insertion sites and improved electrochemical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfur content is increased to increase capacity of titanium sulfide compound, then charge-discharge capacity is improved, but electrical conductivity is significantly reduced
Solution Approach 1:
The invention creates a composite structure where amorphous titanium sulfide with high sulfur content is combined with conductive materials (such as carbon materials or metallic conductors) to form a composite electrode material. This composite structure allows the high-capacity amorphous sulfide to coexist with conductive phases, thereby maintaining both high charge-discharge capacity and sufficient electrical conductivity that neither component could achieve alone.
2Stability of the object's composition
If crystalline structure is used for metal sulfide, then structural stability is maintained, but charge-discharge reversibility is reduced due to great structural change during lithium insertion/extraction
Solution Approach 1:
The invention changes the structural parameter of the titanium sulfide from crystalline to amorphous state. The amorphous structure lacks the long-range order of crystalline structures, allowing for more flexible accommodation of lithium ions during insertion and extraction cycles. This structural transformation enables the material to undergo smaller effective structural changes during charging and discharging, thereby improving charge-discharge reversibility while maintaining compositional stability.
3Quantity of substance
If elemental sulfur is used as cathode material, then theoretical capacity is very high (about 1,670 mAh/g), but electronic conductivity is low and polysulfide elution occurs
Solution Approach 1:
The invention forms a composite where elemental sulfur or sulfur-rich compounds are combined with titanium sulfide matrix. The titanium sulfide provides a conductive framework and structural support, while sulfur contributes high capacity. The composite structure prevents polysulfide elution by confining sulfur within the titanium sulfide matrix, thereby simultaneously achieving high capacity, improved conductivity, and polysulfide stability.
Solution Approach 2:
The titanium sulfide acts as an intermediary material between elemental sulfur and the electrolyte. It provides a stable matrix that hosts sulfur, mediates electron transport, and prevents direct contact between polysulfides and the electrolyte, thereby eliminating polysulfide elution while maintaining sulfur's high capacity advantage.
4Quantity of substance
If amorphous titanium sulfide is produced to increase capacity, then charge-discharge capacity is improved, but electrical conductivity is significantly reduced
Solution Approach 1:
The invention creates a composite material system where amorphous titanium sulfide (providing high capacity) is combined with conductive additives such as carbon materials (graphite, carbon nanotubes, graphene) or metallic conductors. This composite structure ensures that the electrical conductivity deficiency of amorphous sulfide is compensated by the conductive phase, enabling both high capacity and sufficient conductivity to be achieved simultaneously.
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 amorphous sulfides demonstrate higher charge-discharge capacity, improved electrical conductivity, and reduced capacity loss, enabling their use as effective cathode active materials in lithium batteries, including all-solid-state batteries, while allowing for the use of various solvents without performance degradation.
Implementation Method 1
produced through mechanical milling of niobium, titanium, sulfur, and lithium sources
Implementation Method 2
the sites of crystalline metal sulfide into which Li can be inserted during discharging are defined by crystal space groups
Implementation Method 3
a crystalline metal sulfide and/or a carbon-containing material is present in a matrix of amorphous sulfide
Data Source
AI summary
The sulfide of the present invention comprises an amorphous (lithium) niobium sulfide having an average composition represented by formula (1): Lik1NbSn1 (wherein 0≤k1≤5; 3≤n1≤10; and when n1≥3.5, k1≤0.5), or an amorphous (lithium) titanium niobium sulfide having an average composition represented by formula (2): Lik2Ti1-m2Nbm2Sn2 (wherein 0≤k2≤5; 0<m2<1; 2≤n2≤10; and when n2≥3.5, k2≤1.5). The sulfide of the present invention is a material that is useful as a cathode active material for lithium batteries, such as lithium primary batteries, lithium secondary batteries, and lithium ion secondary batteries, and has a high charge-discharge capacity, high electrical conductivity, and excellent charge-discharge performance.