Carbon Battery Brine Electrolyte for Low Self-Discharge
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Solution Overview
Problem
Secondary carbon batteries with water-based electrolytes face issues of self-discharge at elevated voltages due to thermodynamic instability and oxidative degradation of carbon electrodes, limiting their operating voltage and energy storage efficiency.
Innovation Solution
Employing porous carbon electrodes immersed in a concentrated brine electrolyte comprising binary and ternary eutectic solutions of NaCl, KCl, MgCl2, and CaCl2, with repetitive charge-discharge cycling and electrolyte replacement to enhance operating voltage and reduce self-discharge rates, while using graphite current collectors and activated carbon electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If water-based electrolytes are used in carbon batteries, then environmental benignity and cost are improved, but self-discharge occurs at elevated voltages due to thermodynamic instability
Solution Approach 1:
The patent changes the electrolyte composition parameters by using concentrated brine solutions (high salt concentration) instead of traditional dilute aqueous electrolytes. This parameter change shifts the thermodynamic stability region, allowing the battery to operate at elevated voltages (up to 1.85V) without significant self-discharge, while maintaining environmental benignity through the use of common salts like NaCl, KCl, MgCl2, and CaCl2.
Solution Approach 2:
The patent employs composite electrode structures combining porous carbon materials with conductive additives and surface modifications. This composite approach creates a more stable electrode-electrolyte interface that reduces parasitic reactions and self-discharge, while the porous carbon structure provides high surface area for charge storage.
2Use of energy by moving object
If operating voltage is increased above thermodynamic stability region, then energy density is improved, but oxidative degradation of carbon electrodes occurs
Solution Approach 1:
The patent changes the electrolyte concentration parameter to create concentrated brine solutions, which expands the electrochemical stability window and allows operation at higher voltages (up to 1.85V) without water decomposition. This enables higher energy density while preventing oxidative degradation through the altered thermodynamic environment.
Solution Approach 2:
The patent applies surface modification treatments to the carbon electrodes, creating different surface properties (local quality) that enhance stability. Surface treatments such as oxidation, alkaline washing, or coating with conductive materials protect specific regions of the electrode from oxidative degradation while maintaining overall electrode performance.
3Quantity of substance
If surface modification of electrodes is applied, then capacity is improved, but self-discharge rates increase due to enhanced reactivity
Solution Approach 1:
The patent changes the electrolyte concentration parameter to concentrated brine solutions, which suppresses self-discharge even when electrodes undergo surface modification. The high ionic strength and altered solvation environment of concentrated electrolytes reduce parasitic reactions at modified electrode surfaces, allowing capacity enhancement without penalty in self-discharge.
Solution Approach 2:
The concentrated brine electrolyte acts as an intermediary medium that mediates between the modified electrode surface and the external environment. It provides a stable interface that reduces direct contact between reactive electrode surfaces and water, thereby minimizing self-discharge while allowing the modified surfaces to maintain their enhanced capacity.
4Stability of the object's composition
If relative size of positive electrodes is increased, then oxidative stress is reduced, but device complexity increases
Solution Approach 1:
The patent changes the electrolyte composition to concentrated brine solutions, which fundamentally alters the stability characteristics of the system. This parameter change allows the use of simpler, symmetric electrode configurations (equal size positive and negative electrodes) while maintaining stability, eliminating the need for complex asymmetric designs.
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
Achieves an operating voltage of up to 1.85 V with reduced self-discharge rates, improving energy storage capacity and stability, making the batteries suitable for renewable energy storage applications.
Implementation Method 1
Charge-discharge cycle in these batteries relies in part on the reversible electrochemical redox reactions on the surface of porous carbon electrodes
Implementation Method 2
as well as capacitance and pseudo-capacitance of these electrodes
Implementation Method 3
Employing porous carbon electrodes immersed in a concentrated brine electrolyte comprising binary and ternary eutectic solutions of NaCl, KCl, MgCl2, and CaCl2
Data Source
AI summary
Secondary carbon batteries are attractive from an environmental perspective, as they have carbon-only electrodes and are therefore metal-free. Current invention refers to novel secondary carbon batteries with water-based brine electrolytes. These electrolytes have low toxicity, are not flammable, and allow for easy on-site battery recycling. The inventive carbon batteries feature graphite current collectors, activated carbon electrodes, and aqueous eutectic electrolytes comprising NaCl, KCl, MgCl2, or CaCl2). Further improvement of the batteries is performed by an initial repetitive charge-discharge cycling with subsequent replacement of the spent electrolyte. The improved secondary carbon batteries with the operating voltage of about 1.8 V can be used for electric storage utilities of renewable energy installations.