High Performance TiP₂O₇Based Intercalation Negative Electrode for Aqueous Lithium-Ion Batteries via a Facile Synthetic Route

Abstract

A composite TiP 2 O 7 /amorphous carbon material (C-TiP 2 O 7 ) was prepared by an intensive mechanical mixing/solid-state synthesis method at 800 • C. Physical properties were characterized via powder X-ray diffraction, Rietveld refinement, SEM, BET and TGA. Electrochemical performance was evaluated in both a three electrode test setup and two electrode coin cells via cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic cycling tests. The C-TiP 2 O 7 composite demonstrated excellent cycling performance in 1 M Li 2 SO 4 when matched with LiMn 2 O 4 as a positive electrode: when cycled at C/2 for 150 cycles, the capacity retention is over 91% with coulombic efficiencies exceeding 99%. The initial discharge capacity obtained at a C/10 rate is 91 mAh/g which is about 75% of theoretical capacity 121 mAh/g. The apparent diffusion coefficient of C-TiP 2 O 7 composite calculated from cyclic voltammetry result is 3. 3-6 However these materials typically suffer from inherently low electronic conductivity.2 Several strategies such as carbon coating, doping and conductive polymer coating have been developed to improve the electrochemical performance of polyanion-based materials for battery applications. 7-19A less explored phase, TiP 2 O 7 , is not a promising cathode candidate for lithium-ion battery due to its low redox potential of 2.6 V versus Li/Li + . 20,21 However, this redox potential makes TiP 2 O 7 an ideal anode material candidate for aqueous lithium-ion batteries, 22,23 which have been recently explored by several research groups. 21,22 TiP 2 O 7 has a 3D framework structure with a corner sharing a TiO 6 octahedra and a PO 4 tetrahedra, and a phase change reaction between TiP 2 O 7 and LiTiP 2 O 7 . [20][21][22][23][24][25][26][27] Such an open frame structure enables rapid Li + insertion and extraction and good thermal stability. However, the low electronic conductivity remains a major hurdle for its practical applications.23,26 A carbon coating on TiP 2 O 7 can serve two purposes: (1) it improves the kinetics of electron transfer, and (2) [22,28]. However, they found that their cells had limited cycling performance due to the dissolution of TiP 2 O 7 over time.Combining high energy mechanical alloying with intimate carbon coating has proven effective in improving electrochemical performance of polyanion-based materials. 19,[29][30][31][32] Ball milling with intimate carbon helps to prepare a homogenous mixture of precursors and reduce particle size during following thermal treatment. In addition, this combination can decrease the thermal treatment time needed. In this study, we demonstrated C-TiP 2 O 7 composite prepared by high energy mechanical alloying combined with intimate carbon coating has superior cycling performance in aqueous lithium-ion electrolyte. * Electrochemical Society Active Member.z E-mail: whitacre@andrew.cmu.edu ExperimentalSynthesis of electrode materials.-The kinetically assisted synthesis process includes following steps: (1) the precursors for synthesizing C-Ti...

Flexible Ultrafast Aqueous Rechargeable Ni//Bi Battery Based on Highly Durable Single‐Crystalline Bismuth Nanostructured Anode

“…Apparently, the Bi‐200 electrode exhibits an extremely outstanding rate capability with remarkable specific capacities ranging from 96.2 mA h g −1 (64 μA h cm −2 ) at 4.5 A g −1 (3 mA cm −2 ) to 90.5 mA h g −1 (60.2 μA h cm −2 ) at 45 A g −1 (30 mA cm −2 ). These values are substantially larger than those of the untreated Bi electrode (58.8 mA h g −1 , 42.5 mA h g −1 ) and other previously reported anodes for aqueous rechargeable batteries, such as LiV 3 O 8 (21 mA h g −1 at 1 mA cm −2 ), MoO 3 (60 mA h g −1 at 1 A g −1 ), TiO 2 (75 mA h g −1 at 4 mA cm −2 ), and C–TiP 2 O 7 (91 mA h g −1 at 0.0121 A g −1 ) . Indeed, the Bi‐200 electrode could maintain an ultrahigh capacity retention of 93.9% as the discharge current increased from 4.5 to 45 A g −1 , which is considerably superior to the untreated Bi electrode (72.3%) and other reported anodes .…”

Systems-level investigation of aqueous batteries for understanding the benefit of water-in-salt electrolyte by synchrotron nanoimaging

“…However, the limited voltage window for water of ~1.23 V has impeded the development of practical highvoltage aqueous battery technology for more than 20 years. Through fine-tuning of pH values and other electrolyte parameters, stable cycling of some electrode couples in aqueous Li-ion batteries such as LiMn 2 O 4 -LiTi 2 (PO 4 ) 3 and LiMn 2 O 4 -TiP 2 O 7 with cell voltages of ~1.5 V has been realized (3)(4)(5). However, the voltage range is still far from being competitive, with commercial Li-ion batteries with nonaqueous electrolytes operating at >3.5 V.…”

High‐Energy Aqueous Lithium Batteries

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research, aqueous electrolytes were occasionally employed for the investigation of cathode materials instead of the conventional nonaqueous electrolytes. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] A possible reason is that the key advantage of ARLBs was low cost, and thus, the focus was limited to a few inexpensive materials (e.g., lithium salts). For instance, although the formation of solid electrolyte interphase (SEI) is of utmost importance for the cyclability of LIB, the significant role of the electrolyte does not allow to exclusively study the electrochemical behavior of the electrode material under consideration.

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