Organic Dicarboxylate Negative Electrode Materials with Remarkably Small Strain for High‐Voltage Bipolar Batteries

Abstract

As advanced negative electrodes for powerful and useful high-voltage bipolar batteries, an intercalated metal-organic framework (iMOF), 2,6-naphthalene dicarboxylate dilithium, is described which has an organic-inorganic layered structure of π-stacked naphthalene and tetrahedral LiO4 units. The material shows a reversible two-electron-transfer Li intercalation at a flat potential of 0.8 V with a small polarization. Detailed crystal structure analysis during Li intercalation shows the layered framework to be maintained and its volume change is only 0.33%. The material possesses two-dimensional pathways for efficient electron and Li(+) transport formed by Li-doped naphthalene packing and tetrahedral LiO3C network. A cell with a high potential operating LiNi(0.5)Mn(1.5)O4 spinel positive and the proposed negative electrodes exhibited favorable cycle performance (96% capacity retention after 100 cycles), high specific energy (300 Wh kg(-1)), and high specific power (5 kW kg(-1)). An 8 V bipolar cell was also constructed by connecting only two cells in series.

Improvement in the Electrochemical Properties of Intercalated Metal–Organic Framework Electrode Materials by Controlling Crystal Growth

“…2 For comparison, 2,6-Naph(COOLi) 2 was also synthesized under aqueous conditions via the same procedure used for synthesis under methanol. XRD patterns of the respective 2,6-Naph(COOLi) 2 samples were obtained using a Rigaku RINT-TTR diffractometer equipped with a Cu-KA radiation source operated at 50 kV and 300 mA; the samples were scanned over the range 10°¯2ª CuKA¯5 0°in reflection mode.…”

“…3 The 2,6-Naph(COOLi) 2 electrode exhibits a reversible two-electrontransfer Li intercalation reaction (220 mAh g ¹1 ) at a flat potential of 0.8 V and maintains its framework structure, exhibiting remarkably small volume strain (0.33%) during Li intercalation. 2 Furthermore, the proposed material exhibits improved regularity of O-stacked packing via self-organization induced by heat treatment under inert atmosphere; this improved packing led to an improvement of reversible capacity as well as to a reduction of internal resistance. 4 Although similar electrode materials have been extensively reported by other groups, [5][6][7] little consideration has been given to the detailed understanding of the relationship between electrochemistry and crystal structure to the MOF based electrode materials.…”

“…We have prepared a novel intercalated metal-organic framework (iMOF) electrode material, 2,6-naphthalene dicarboxylate dilithium (2,6-Naph(COOLi) 2 ), which operates in the potential range of 0.5-1.0 V (vs. Li/Li + ), as a next-generation negative electrode material for advanced lithium-ion batteries. Further, we investigated its crystal structure and basic electrochemical behavior.…”

“…In addition, because Al can be used as a current collector for this iMOF negative electrode material, whose operating potential is more positive than the potential of the Li-Al alloy reaction (0.4 V), it can potentially be used as a negative electrode material in high-voltage bipolar batteries using only Al current collector. 2 As shown in Fig. 1, this material has an organic-inorganic layered crystal structure composed of O-stacked naphthalene packing layers and tetrahedral LiO 4 network units, respectively.…”

“…4 Although similar electrode materials have been extensively reported by other groups, [5][6][7] little consideration has been given to the detailed understanding of the relationship between electrochemistry and crystal structure to the MOF based electrode materials. In this work, we further investigate the Li intercalation characteristics in each crystal plane of the 2,6-Naph(COOLi) 2 and discuss the improvement of its electrochemical properties via control of its crystal growth. …”