Geminal Dinitrile Electrolytes for Stable Primary Alkali Metal Cells
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Solution Overview
Problem
Primary alkali metal cells face issues with the deposition of alkali metals and cathode material on the anode surface and inner surfaces, leading to voltage delays and reduced performance, especially in long-term and high-current applications such as medical devices, due to the formation of a high-ohmic solid-electrolyte interphase (SEI) and irregular deposition patterns.
Innovation Solution
Incorporating nonionic or ionic compounds with a geminal dinitrile moiety into the electrolyte, such as aliphatic heterocycles or specific compounds like tetracyanoethylene, which form a stable SEI, preventing the deposition of alkali metals and cathode materials on the anode surface and minimizing impedance, thus maintaining consistent discharge behavior even under high-rate and high-current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If alkali metal is used as active anode material to achieve high specific capacity and high nominal voltage, then the theoretical specific capacity and voltage are improved, but a passivation layer (SEI) forms on the anode surface which increases cell impedance and reduces discharge voltage and battery capacity
Solution Approach 1:
A geminal dinitrile compound is introduced as an intermediary substance in the electrolyte that mediates between the alkali metal anode and the electrolyte. This compound preferentially reacts with the alkali metal to form a modified SEI layer that is more ionically conductive than the conventional SEI, thereby reducing impedance while maintaining the protective function. The dinitrile compound acts as a sacrificial additive that modifies the SEI composition and structure.
Solution Approach 2:
The invention changes the chemical composition parameters of the electrolyte by adding geminal dinitrile compounds (such as tetracyanoethylene or 1,1,2,2-tetracyanoethylene) at specific concentrations (0.01-10 mM). This parameter change alters the SEI formation process, leading to an SEI layer with different ionic conductivity properties. The addition of these compounds modifies the electrochemical window and reaction kinetics at the anode surface.
2Reliability
If the SEI layer is formed to prevent further degradation reactions, then the stability of the anode surface is improved, but the low ionic conductivity of the SEI results in an increase of impedance inside the cell
Solution Approach 1:
The geminal dinitrile compound serves as an intermediary that modifies the SEI layer composition. It reacts with the alkali metal to form a SEI layer enriched with dinitrile decomposition products that have higher ionic conductivity. This intermediary substance transforms the SEI from a low-conductivity protective layer to a dual-function layer that maintains stability while enabling ion transport.
Solution Approach 2:
The SEI layer becomes a composite structure containing conventional SEI components (such as alkali metal halides and oxides) combined with dinitrile-derived species. This composite SEI layer exhibits synergistic properties: the conventional components provide structural stability and protection, while the dinitrile-derived components provide ionic conductivity pathways, achieving both stability and low impedance.
3Duration of action of stationary object
If alkali metals are used in long-term storage applications to maintain stable performance, then the low self-discharge rate is improved, but voltage delay occurs under pulse discharge conditions after elongated storage or inactivity periods
Solution Approach 1:
The geminal dinitrile compound performs a preliminary action during initial cell formation and storage by pre-modifying the SEI layer before pulse discharge conditions occur. This preliminary modification ensures that when pulse discharge conditions arise after storage, the SEI is already in an optimized state with appropriate ionic conductivity, preventing voltage delay. The dinitrile additive proactively prepares the anode surface for subsequent high-rate discharge.
Solution Approach 2:
The invention changes the temporal parameters of SEI stability by using dinitrile compounds that form a progressively stable SEI during storage. The SEI composition evolves over time in the presence of dinitrile, becoming more conductive and stable, which eliminates voltage delay even after extended storage periods. This parameter change in SEI evolution kinetics resolves the contradiction between storage stability and pulse discharge performance.
4Object-affected harmful factors
If the electrolyte composition is modified to reduce SEI impedance, then the ionic conductivity is improved, but the stability of the SEI layer may be compromised
Solution Approach 1:
The geminal dinitrile compound acts as a stabilizing intermediary that reconciles the conflict between ionic conductivity and SEI stability. It forms a SEI layer where dinitrile-derived species create conductive pathways without compromising the overall structural integrity. The dinitrile molecule serves as a bridge between the alkali metal and the electrolyte, creating an intermediate SEI composition that achieves both conductivity and stability.
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 addition of geminal dinitrile compounds stabilizes the SEI, suppressing alkali metal deposition, eliminating voltage delays, and enhancing the reliability and lifespan of primary alkali metal cells, ensuring consistent performance even after extended periods of non-use or high depth of discharge.
Implementation Method 1
the formation of a passivation layer at the anode surface due to reactions with the cell electrolyte. This passivation layer is known solid-electrolyte interphase (SEI)
Implementation Method 2
The formation of metallic lithium deposits occurs if the potential of the respective component is below deposition potential of the respective alkali metal
Implementation Method 3
the electrolyte comprises at least one additive... the electrolyte comprises at least one conductive salt selected from the group consisting of inorganic salts and organic salts
Data Source
AI summary
The invention belongs to a primary cell. Said primary cell contains at least one anode, with an alkali metal as active anode material, at least one cathode with an active cathode material and an electrolyte. Additionally the electrolyte comprises at least one additive whereby it is in accordance with the inventive idea that the at least one additive is a nonionic or ionic compound having at least one geminal dinitrile moiety and is selected from the group consisting of aliphatic heterocycles, compounds of the formulawherein My+ denotes a counterion with a valence of y, and wherein R, R′ and R″ are substituents with an aliphatic or aliphatic heterocyclic backbone.