3D Hierarchical nano-flake/micro-flower iron fluoride with hydration water induced tunnels for secondary lithium battery cathodes

Abstract

As a potential multi-electron electrode material for next generation lithium ion batteries, iron fluoride (FeF 3 ) and its analogues are attracting much more attentions. Their microstructures are the key to achieve good electrochemical performances. In this work, FeF 3 ·3H 2 O nano-flakes precursor with high crystallinity and flower-like morphology is synthesized successfully, by a liquid precipitation method using Fe(NO 3 ) 3 ·9H 2 O and NH 4 HF 2 as raw materials. The formation and the crystal growth mechanisms of the FeF 3 ·3H 2 O precursors are investigated and discussed. After different temperature heat-treatment and followed by ball-milling with Super P, the as-prepared FeF 3 ·0.33H 2 O/C and FeF 3 /C nanocomposites are used as cathode materials for lithium ion batteries. The FeF 3 ·0.33H 2 O/C nanocomposite exhibits a noticeable initial specific capacity of 187.1 mAh g -1 and reversible specific capacity of 172.3 mAh g -1 at 0.1C within a potential range of 2.0-4.5V. The capacity retention is as high as 97.33% after 50 cycles. Combined with HRTEM test, it confirms that the hydration water is not harmful but useful, namely, the tunnel phase formed with the hydration water is crucial to unobstructed Li + diffusion, and therefore leading to excellent electrochemical performances.

Improved Electrochemical Performance of FeF3 by Inlaying in a Nitrogen‐Doped Carbon Matrix

“…Therefore, the efficient storage of energy is also a severe challenge. [7] Transition metal fluorides as conversion-type cathode materials are regarded as the most promising candidate for the next generation of cathodes. So, it is widely used for portable handheld devices, electric vehicle and other large-scale application systems, etc.. [1,3] However, the low specific capacities of traditional intercalated electrode materials cannot be satisfied the eager demand of high capacity.…”

“…[5,8] Among them, iron fluoride (FeF 3 ) has been widely studied because the high theoretical capacity of 712 mAh g À 1 (delivering three electrons) and working potential (about 3.0 V for the redox reaction). Researchers have made great efforts to overcome these defects, such as morphology and structure regulation, [7,[14][15][16][17] nano-refinement, [7,14,18,19] developing derivatives of FeF 3 , [6,[20][21][22] doping metal atoms [22][23][24] and combining FeF 3 nanoparticles with conductive materials. [10][11][12] However, the strong ionic character of FeÀ F bonds lead to poor electronic conductivity and inferior kinetics, which greatly limits the capacity for storing lithium.…”

“…[4][5][6] In this case, the conversion reaction involving multiple-electrons have received much attention because it can deliver high specific capacity. [7] Transition metal fluorides as conversion-type cathode materials are regarded as the most promising candidate for the next generation of cathodes. [5,8] Among them, iron fluoride (FeF 3 ) has been widely studied because the high theoretical capacity of 712 mAh g À 1 (delivering three electrons) and working potential (about 3.0 V for the redox reaction).…”

Investigations of aluminum fluoride as a new cathode material for lithium-ion batteries

“…Many research groups reported in the 1990s a small reversible capacity of 80 mAh g −1 for FeF 3 . The electrochemical reaction of the conversion mechanism was shown by these groups to be very rate and temperature sensitive [7][8][9]. This is due to the structural decomposition and reconstruction of the metal fluoride as well as the transport of the lithium ions in the bulk phase.…”

Iron Fluoride Packaged into 3D Order Mesoporous Carbons as High-Performance Sodium-Ion Battery Cathode Material

“…6,7 Among the various SIBs cathode materials, iron-based fluorides, such as FeF 3 , FeF 3 · 0.5H 2 O, Fe 2 F 5 · H 2 O and FeF 3 · 0.33H 2 O, have caused tremendous interest due to high operational voltage (average ∼2.74 V vs. Na/Na + ), nontoxicity and low-cost. 8 Especially, in the family of iron-based fluorides, the nanoscale FeF 3 · 0.33H 2 O has a great prospect because its unique tunnel structure and high theoretical specific capacity. The tunnel structure is beneficial to electrolyte ion penetration, Na + transport, and interfacial processes.…”