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Double Carbon Battery Based On Potassium Electrolyte

- Jan 09, 2019 -

Lithium-ion batteries (LIBs) now dominate the field of electrochemical energy storage in portable electronic devices, electric vehicles (EVs) and smart grids. However, the shortage of lithium resources, uneven geographical distribution and rising costs have become urgent problems to be solved. Therefore, abundant and low-cost new battery systems, such as sodium ion battery (SIBs), aluminum ion battery (AIBs) and double ion battery (DIBs), have attracted extensive attention from scientists. Potassium ion batteries (KIBs) also have great application potential because of their similar properties to lithium and abundant reserves. Compared with SIBs, KIBs provides higher operating voltage because of its lower REDOX potential. In addition, K+ has been shown to reversibly embed/de-embed graphite electrodes, while Na+ is very limited. However, research on KIBs is still in its infancy, and the mechanisms of atomic scale and interface remain unclear. In addition, due to the large size deviation of K+, the dynamics was unstable. Only a few positive pole materials (Prussian blue and its analogues, etc.) and negative pole materials (graphite, Sn4P3/C, etc.) could be studied. Therefore, it is very important to develop suitable electrode materials with good properties and comprehensively study the mechanism of KIBs.

Recently, shenzhen institutes of advanced technology Tang Yongbing researcher of Chinese academy of sciences (corresponding author) group in Adv. Energy Mater., published A paper entitled "A Dual - Carbon '-based on Potassium - Ion Electrolyte" articles. The researchers developed a new type of dual-carbon battery (named k-dcb) based on potassium electrolyte, in which intermediate carbon microspheres are used as the cathode material and expanded graphite as the anode material. The experimenters studied the working mechanism of k-dcb: during charging, K+ moved to the graphite negative electrode and embedded into the graphite interlayer to form intercalation compound; meanwhile, PF6- moved to the positive electrode and intercalation layer was inserted into the interlayer of the intermediate phase carbon microsphere. Discharge is the opposite. The results show that the k-dcb can provide 61mAh g-1 reversible specific capacity in the voltage window range of 3.0-5.2v and the current density of 1C, and has good cycling performance. After 100 cycles, the capacity has almost no attenuation. In addition, the k-dcb has a high median discharge voltage (4.5v), which can meet the requirements of some high-voltage equipment. K-dcb has the advantages of environmental protection, low cost and high energy density, and has great potential for future energy storage applications.

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Schematic diagram of k-dcb charge-discharge mechanism based on potassium electrolyte

A) schematic diagram of k-dcb charging and discharging mechanism of electrolyte containing potassium ions

B) charging and discharging curves under 1C

C) corresponding dQ/dV differential curve

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PF6- process analysis of embedded/de-embedded anode graphite layers

A) non-in-situ XRD of the EG positive electrode recorded in the first charge-discharge cycle at 1C current density

B) non-in-situ Raman spectra of EG positive electrode recorded in the first charge-discharge cycle with 1C current density

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Electrochemical analysis of k-dcb based on 1 M KPF6 / (EC: DMC: EMC = 4:3:2)

A) charging and discharging curves of the battery at different current densities of 1, 2 and 3C

B) charging and discharging capacities and corresponding coulomb efficiency at different current densities

C) cycling performance of k-dcb for 100 cycles at 1C

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Cyclic performance analysis of K-DCB

A) charging and discharging curves of k-dcb in the 20th, 50th and 100th cycles

B) before the cycle and after cycles 5, 10 and 30, the Nyquist diagram of k-dcb

C) the median voltage of k-dcb with 100 cycles under 1C.

The researchers developed a k-dcb based on an interphase carbon microsphere negative electrode and an expanded graphite positive electrode, with an electrolyte of 1 M KPF6/EC+DMC+EMC (4:3:2 v/v/v). The working mechanism of k-dcb involves the embedding/de-embedding process of K+ on the negative electrode of MCMB and the embedding/de-embedding process of pf6-anion on the positive electrode of EG. K-dcb shows good structural stability and excellent cyclic performance. Due to its environmental friendliness, high security, low cost and relatively high energy density, k-dcb has the potential to become the next generation of renewable energy storage equipment.