Graphite Anode for Potassium Ion Batteries: Current Status and Perspective

Abstract

Currently, the commercial Li-ion batteries (LIBs) have received much attention and hold a dominant position in portable device and electric vehicles fields. [1][2][3] However, the shortage of Li resources (only 20 ppm reserves in the crust) and uneven geographical distribution (mainly distributed in South America) result in the high price of LIBs. [4][5][6] With the growing demand of energy storage system, especially for the large-scale fixed power supply applications, LIBs will struggle to compete economically in large-scale energy storage system. [7] These challenges underlie further research into alternative, sustainable, and inexpensive battery technologies. Compared with Li resources, the abundance of Na and K in the crust appears to be infinite, as shown in Figure 1a. [8,9] In the past years, Na-ion batteries (NIBs) have received much attention, which should be due to the similar reaction mechanism to LIBs. [10][11][12] Due to the relatively high standard reduction potential of Na/Na + (−2.71 V vs standard hydrogen electrode [SHE]), NIBs always suffer the low energy density, which astricts the further practical applications. [13][14][15] Considering this issue, K-ion batteries are also raised, which should be due to the relatively low standard reduction potential of K/K + (−2.93 V vs SHE), closing to that of Li/Li + (−3.04 V vs SHE), as shown in Figure 1b. [16,17] This result indicates that KIBs will present higher energy density than that of NIBs. In addition, compared with Li-ion (4.8 Å) and Na-ion (4.6 Å), K-ion always presents a smaller Stokes' radius of (3.6 Å) in conventional propylene carbonate solvent (Figure 1d), illustrating that a higher ion conductivity and mobility can be received in battery system. [18] Therefore, KIBs also have won lots of attention and the publications involving KIBs have been rapidly raised, as shown in Figure 1c. Figure 1f shows the schematic illustration of KIBs, which presents the "rocking-chair" working mechanism of K-ion storage. [19] The K-ion acts as the shuttles, which is exchanged between the cathode and the anode. During the charging process, the K-ion is deintercalated from cathode and then intercalate into the interlamination of anode, which accompanies with the energy storage. While the depotassiation process, an inverted reaction happens, which is along with the energy supply. However, compared with the sizes of Li-ion (0.76 Å) and Na-ion (0.97 Å), the oversize of K-ion (1.38 Å) always leads to the distinct structure damage of anode materials during the potassiation-depotassiation process, which will trigger the obvious capacity decay in the subsequent cycles. [20] Therefore, developing high-performance anode materials for KIBs becomes an important goal in energy storage field.Currently, large numbers of anode materials including metals, oxides, sulfides, phosphides for KIBs have been reported, which present superior performance for K-ion storage. [21][22][23][24][25][26] In spite of these, the cycling stability and the relatively higher voltage plateau also r...

A review of hard carbon anode: Rational design and advanced characterization in potassium ion batteries

“…Galvanostatic intermittent titration technique (GITT) is an approach that combines the advantages of steady‐state technology and transient technology, which evaluates the D values during different potassiation–depotassiation processes. The D values can be calculated by the following equation 38,39 : where τ is the constant‐current pulse time; m and M are the mass and molar mass of the electrode material, respectively; and V m and S are the molar volume and the electrode surface area that contacts electrolyte, respectively. V m is considered constant during the charge and discharge process.…”

Strategies for the Analysis of Graphite Electrode Function

“…Of these, recent reviews have broadly discussed the range of potential strategies to improve performance, [5b,11] as well focused on more specific subjects such as graphite capacity improvement via Si-doping/mixing, [6,12] electrolyte and SEI function/chemistry, [13] thermal stability and safety, [14] graphite as positive electrode, [15] and the intercalation chemistry/compatibility with Na-and K-ion batteries. [16] In addition, reviews have been published on the mining and processing graphite, [17] as well as on possible strategies for recycling used graphite electrodes. [18] However, only limited attention is given to the involved characterization techniques and analytical strategies (despite the continuous innovation and considerable advances in the space) that provide the foundation for obtaining deeper understanding of material function, which may help facilitate the rational design of next-generation graphite-based anodes.…”

In Situ Monitoring the Potassium-Ion Storage Enhancement in Iron Selenide with Ether-Based Electrolyte

“…Because of the low cost and stability, enormous efforts are mainly focused on the carbonaceous materials, which have become the primary selectivity for KIBs [ 13 – 15 ]. However, low theoretical capacities of carbonaceous materials restrict the further improvement in the K-ion storage performance, forcing scientists to explore other high-performance host materials [ 16 , 17 ].…”