Reversible K⁺-Insertion/Deinsertion and Concomitant Na⁺-Redistribution in P′3-Na_0.52CrO₂ for High-Performance Potassium-Ion Battery Cathodes

Abstract

P′3-type Na0.52CrO2 is proposed as a viable cathode material for potassium-ion batteries (KIBs). The in-situ-generated title compound during the first charge of O3-NaCrO2 in K+-containing electrolytes can reversibly accommodate 0.35 K+-ions with no interference with Na+. In addition to the sequential interlayer slippage that occurs with Na+-insertion, K+-insertion into Na0.52CrO2 induces a sudden phase separation, which ultimately results in a biphasic structure when fully discharged (K+-free O3-NaCrO2 and K+-rich P3-K0.6Na0.17CrO2). A reversible transition between monophasic (Na0.52CrO2) and biphasic states during repeated K+-insertion/deinsertion is also maintained, which contributes to superior electrochemical properties of the title compound when used as a KIB cathode. Na0.52CrO2 delivers a specific capacity of 88 mA h g–1 with an average discharge potential of 2.95 V versus K/K+. This high level of energy density (260 W h kg–1 at 0.05C) is not substantially decreased at fast C-rates (195 W h kg–1 at 5C). When cycled at 2C, the first reversible capacity of 77 mA h g–1 gradually decreases to 52 mA h g–1 during initial 20 cycles, but no further capacity fading is observed for subsequent cycles (51 mA h g–1 after 200 cycles). Density-functional-theory computation reveals that the rearrangement of Na+ is an energetically favored process rather than a homogeneous distribution of Na+/K+.

Development of P3-K0.69CrO2 as an ultra-high-performance cathode material for K-ion batteries

“…[11][12][13][14] However, the larger size of K + ions (B1.38 Å) relative to Li + ions (B0.76 Å) and Na + ions (B1.02 Å) makes it difficult to identify high-energy and high-rate intercalation cathode materials. Although a few initial studies have demonstrated the electrochemically reversible potassium (de)intercalation reaction, the cycling stability and rate capability were unsatisfactory for efficient battery applications.…”

“…S7, ESI †). 14,15 This indicated that the electrochemical Na + /K + ion exchange was not yet completed after 50 cycles.…”

Electrochemical Exchange Reaction Mechanism and the Role of Additive Water to Stabilize the Structure of VOPO4⋅2 H2O as a Cathode Material for Potassium‐Ion Batteries

“…[6] Aluminum can be used insteado f copper as ac urrent collector for the anode because potassium metal does not form an alloy with aluminum, providing another cost-reduction benefit. So far,o nly af ew materials have been reported, such as KVPO 4 F, [8] KVOPO 4 , [8] KTi 2 (PO 4 ) 3 , [9] K 3 V 2 (PO 4 ) 3 , [10] KVP 2 O 7 , [11] Prussian-blue analoguesK x MFe(CN) 6 ·y H 2 O( M= transition metal), [12] Na 0.52 CrO 2 , [13] K 0.5 V 2 O 5 , [14] K 0.3 MnO 2 , [7] K x CoO 2 , [15] MoS 2 , [16] TiS 2 , [17] K 0.7 Fe 0.5 Mn 0.5 O 2 , [18] 3,4,9,10-perylene-tetracarboxylic acid-dianhydride (PTCDA), [19] and poly(anthraquinonyl sulfide) (PAQS). So far,o nly af ew materials have been reported, such as KVPO 4 F, [8] KVOPO 4 , [8] KTi 2 (PO 4 ) 3 , [9] K 3 V 2 (PO 4 ) 3 , [10] KVP 2 O 7 , [11] Prussian-blue analoguesK x MFe(CN) 6 ·y H 2 O( M= transition metal), [12] Na 0.52 CrO 2 , [13] K 0.5 V 2 O 5 , [14] K 0.3 MnO 2 , [7] K x CoO 2 , [15] MoS 2 , [16] TiS 2 , [17] K 0.7 Fe 0.5 Mn 0.5 O 2 , [18] 3,4,9,10-perylene-tetracarboxylic acid-dianhydride (PTCDA), [19] and poly(anthraquinonyl sulfide) (PAQS).…”

P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

“…The starting Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 had an interlayer distance of 5.5 Å, whereas the electrochemically formed P2‐K 0.75 [Ni 1/3 Mn 2/3 ]O 2 had a larger interlayer distance (≈6.5 Å). This difference indicates that the large ionic size of K + (1.38 Å) relative to that of Na + (1.02 Å) is responsible for the enlargement of the interlayer distance …”