Potassium Prussian Blue Nanoparticles: A Low‐Cost Cathode Material for Potassium‐Ion Batteries

Abstract

Potassium-ion batteries (KIBs) in organic electrolytes hold great promise as an electrochemical energy storage technology owing to the abundance of potassium, close redox potential to lithium, and similar electrochemistry with lithium system. Although carbon materials have been studied as KIB anodes, investigations on KIB cathodes have been scarcely reported. We for the first time report a comprehensive study on potassium Prussian blue K0.220Fe[Fe(CN)6]0.805·4.01H2O nanoparticles as a potential cathode material. The cathode exhibits a high discharge voltage of 3.1~3.4 V, high reversible capacity of 73.2 mAh g-1 , and great cyclability at both low and high rates with a very small capacity decay rate of ~0.09% per cycle. Electrochemical reaction mechanism analysis identifies the carboncoordinated Fe III /Fe II couple as redox-active site and proves structural stability of the cathode during charge/discharge. Furthermore, for the first time, we present a KIB full-cell by coupling the nanoparticles with commercial carbon materials. The full-cell delivers a capacity of 68.5 mAh g-1 at 100 mA g-1 and retains 93.4% of the capacity after 50 cycles. Considering the low cost and material sustainability as well as the great electrochemical performances, this work may pave the way towards more studies on KIB cathodes and trigger future attention on rechargeable KIBs.

Rechargeable potassium-ion batteries with honeycomb-layered tellurates as high voltage cathodes and fast potassium-ion conductors

“…They constitute the broad class of polyanionic compounds that show high voltage coupled with excellent thermal stability. A flurry of reports in recent years have also emerged on the use of organic moieties such as Prussian analogues as cathode hosts for K-ion 34–38 , as they not only are of low cost, but can also deliver relatively high voltage at moderate capacities. Layered transition metal oxide analogues of classic Li- and Na-ion cathodes, for instance, K x MnO 2 39,40 , K x CoO 2 41,42 , etc.…”

Recent Progress and Perspective in Electrode Materials for K‐Ion Batteries

“…[18,19] These materials are commonly synthesized by precipitation, with the K content (x) ranging from 0 to 2 in K x M A [M B (CN) 6 ]; in addition, the M A content can be tailored by selecting appropriate oxidation states of the M A precursors. For example, KFe[Fe(CN) 6 ] is precipitated when FeCl 3 is added to an aqueous K 4 Fe(CN) 6 solution, [82] and K 2 Mn[Fe(CN) 6 ] is precipitated when Mn(NO 3 ) 2 is added to an aqueous K 4 Fe(CN) 6 solution. [83] However, crystal water from the synthesis tends to be incorporated into the structure, replacing the entire [M B (CN) 6 ] unit or occupying the interstitial site, as illustrated in Figure 7b, [81,84] leading to a composition that should be reported as K x M A [M B (CN) 6 ] 1−z -nH 2 O.…”

“…[88] The cubic-to-tetragonal transition, on the other hand, can be explained by the JahnTeller distortion caused by the high-spin Mn 3+ . [88] Note that when the M A site is occupied by Jahn-Teller inactive elements such as high-spin Fe 3+ , the cubic-to-tetragonal phase transformation is unobservable; [82,83] and instead a solid-solution type intercalation reaction occurs.…”

“…[82,83,88,89] Whereas the M B site is generally occupied by Fe, the use of different transition metals for the M A site leads to different K intercalation capacities and rate capability. [20] [88] A reversible discharge capacity of 137 mA h g −1 , which reflects near theoretical K intercalation (1.88 K), is achieved at a cycling rate of 30 mA g −1 .…”

Short‐Range Order in Mesoporous Carbon Boosts Potassium‐Ion Battery Performance

“…[7][8][9] In comparison to the natural abundance of lithium (20 ppm) in the Earth's crust, the abundances of Na (23 000 ppm) and K (17 000 ppm) seem infinite. [13][14][15][16][17] The advantages of KIBs are obvious: the abundant resource and the closer redox potential of K/K + (−2.93 V vs standard hydrogen electrode) to that of Li/Li + (−3.04 V) than that of Na/Na + (−2.71 V), implying their higher voltage plateau and energy density.Different K ion anode materials such as graphite, [13,18,19] nitrogen-doped graphene, [14,20] Prussian Blue, [21][22][23] and transition metal compound [24,25] have been Till last two years, the new concept of KIBs has begun to gain much more attention.…”