Self-discharge in a planish machine for supercapacitors refers to the spontaneous reduction of stored charge and continuous voltage drop in an open-circuit state. This phenomenon not only reduces energy storage efficiency but can also affect system reliability. Its physicochemical processes involve complex interactions between electrodes, electrolytes, and separators, and can be mainly categorized into three mechanisms: leakage current, Faraday reactions, and charge redistribution.
Leakage current is one of the direct causes of self-discharge, essentially resulting from parasitic reactions between the electrolyte and electrode materials or charge loss due to internal micro-short circuits. In planish machines for supercapacitors, the surface of electrode materials (such as carbon-based materials) may have micropores or defects. Electrolyte ions can undergo non-ideal adsorption or chemical reactions with the electrodes through these pathways, forming tiny current paths. Furthermore, defects in the separator or burrs on the electrode edges during assembly can trigger local short circuits, allowing charge to be released directly through internal resistance. This type of self-discharge typically becomes the dominant factor after several hours and is closely related to the packaging process and material purity.
Faraday reactions are the core chemical mechanism of self-discharge, primarily originating from redox reactions on the electrode surface or in the electrolyte. Carbon-based electrode materials often contain oxygen-containing functional groups such as carboxyl and hydroxyl groups on their surface. These groups can undergo reversible or irreversible redox reactions under an electric field, consuming stored charge. For example, oxygen-containing functional groups may weaken the interaction between electrolyte ions and the electrode surface, promoting ion delamination from the electric double layer; dissolved oxygen in the electrolyte may also consume charge through reduction reactions (e.g., O₂ + 2H₂O + 4e⁻ → 4OH⁻). The rate of these reactions is affected by reactant concentration, electrode potential, and temperature, and is generally classified into two categories: activation-controlled (reaction rate determined by reactant concentration) and diffusion-controlled (reaction rate determined by ion migration rate).
Charge redistribution is a physical process of self-discharge and is closely related to the electric double layer structure. The energy storage of a planish machine for supercapacitors is based on the electric double layer formed at the electrode-electrolyte interface, where positive and negative charges are closely arranged on the electrode surface and electrolyte side, respectively. However, this structure is not entirely static: in the open-circuit state, thermal motion may cause some charges to detach from the double layer and redistribute into the electrolyte; simultaneously, charges within the electrode material may migrate due to concentration gradients. While this redistribution process does not involve chemical reactions, it gradually weakens the charge separation of the double layer, leading to a voltage drop.
The surface properties of the electrode material significantly influence self-discharge behavior. For example, the ash content and oxygen-containing functional groups in carbon-based materials accelerate self-discharge, while thermal reduction with hydrogen can reduce the number of functional groups, thereby lowering the self-discharge rate. The type of electrolyte is equally crucial: aqueous electrolytes, due to their high ion mobility and abundant oxygen content, typically exhibit more severe self-discharge than organic electrolytes; ionic liquid electrolytes, with their high viscosity and low volatility, effectively suppress ion diffusion and Faraday reactions. Modification of the membrane (such as introducing positively and negatively charged groups) can further suppress self-discharge by repelling corresponding ions and reducing transmembrane shuttle stress.
Strategies for suppressing self-discharge must balance electrochemical performance and energy efficiency. For example, using ionic liquid electrolytes or adding bentonite can reduce ion mobility, but may sacrifice rate performance; modified membranes, while suppressing ion diffusion, may increase internal resistance. Therefore, modern research tends to achieve a synergistic improvement in self-discharge rate and power density through material design (such as heteroatom doping and surface functionalization) and structural optimization (such as porous electrode modulation).
The self-discharge phenomenon of planish machines for supercapacitors is the result of the combined effects of physical and chemical processes, involving leakage current, Faraday reactions, and charge redistribution. A deeper understanding of these processes not only helps optimize material selection and structural design but also provides theoretical guidance for developing highly reliable energy storage systems. In the future, with further research into the dynamic behavior of the electrode-electrolyte interface, self-discharge suppression technologies will further promote the application of planish machines for supercapacitors in new energy, smart grids, and other fields.
