Differences between lithium-ion capacitors and lithium-ion batteries
The positive and negative active substances of lithium-ion batteries are compounds that can reversibly insert and remove lithium, in which at least one electrode material is in the lithium embedded state before assembly, such as transition metal oxides LiCoO2, LiNiO2 and LiMn2O4 as the positive electrode, and various carbon materials, metal oxides or alloys as the negative electrode materials.
The working principle of lithium-ion battery uses graphite as the negative electrode and LiCoO2 as the positive electrode. During charging, lithium ions are separated from the positive material and migrate to the negative electrode through the electrolyte driven by the electrochemical potential gradient. The charge balance requires an equal amount of electrons to flow from the positive electrode to the negative electrode under the external circuit. After reaching the negative electrode, the lithium ions that get electrons are embedded into the lattice of the negative material; During discharge, the reverse process is followed, that is, lithium ions leave the negative lattice and embed into the positive electrode to form LiCoO2 again. During the charging and discharging process of lithium-ion battery, lithium takes the form of ions (Li +) as the carrier of energy exchange. Through the electrolyte, lithium ions are embedded and removed, swinging between the positive and negative electrodes to achieve the purpose of energy exchange.
The positive material of lithium-ion capacitor is activated carbon material with double-layer energy storage, the negative material is intercalated carbon material with lithium ion de intercalation function, and the electrolyte is lithium salt electrolyte. When the battery is charged, lithium ions are separated from the surface of the positive material, and inserted into the lattice of the negative material after passing through the electrolyte and diaphragm; During discharge, lithium ions are separated from the lattice of the negative material, return to the surface of the positive material through the electrolyte, and form an electric double layer with the charge of the positive material.
Comparison of capacity, voltage and self discharge the energy density of lithium-ion capacitor is less than that of lithium-ion battery, but the output density is high; The energy density of monomer volume is 10~15wh/l, which is much larger than the capacity of electric double-layer capacitor of 2~8wh/l, which is twice that of the latter. In terms of voltage, the maximum voltage of lithium-ion capacitor can reach 4V, which is similar to that of lithium-ion battery, but much higher than that of electric double-layer capacitor. At the same time, it is smaller than both in terms of self discharge. The cathode of safe lithium-ion battery uses lithium oxide, which not only contains a large amount of lithium, which can form lithium dendrites and pierce the diaphragm, but also contains oxygen, an important ignition element. Once the battery is short circuited, it can develop into overall thermal decomposition, and the reaction with electrolyte can cause combustion. The positive pole of lithium-ion capacitor is activated carbon. Even if the internal short circuit will react with the negative pole, it will not react with the electrolyte. Theoretically, it will be much safer than lithium battery. Long service life in order to achieve a long service life, lithium-ion batteries have certain range restrictions on the depth of charging and discharging, which reduces the capacity that can be used in essence. The charge and discharge principle of electric double-layer capacitors has a long service life simply by adsorbing or removing ions from the electrolyte, which is difficult to extend the actual service life.
Post time: Jul-01-2022