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This research aimed to increase the mass loading of sulfur in the composite electrode in order to increase the energy density of the lithium-sulfur (Li-S) cell. This requires designing the electrode with the use of conductive agents to maintain the conductivity of the sulfur composite. Therefore, the composite of sulfur with polyacrylonitrile (PAN) and carbon nanotubes (CNT) was synthesized by heating. Following that, the mass loading of sulfur was increased by using several layers of carbon fiber paper (CFP) with a large free space as a three-dimensional current collector. As a result of the heat treatment and formation of covalent bonding between pyrolyzed PAN and sulfur, uniform distribution and enhanced conductivity were achieved, while CNT maintained structural integrity, acting as an interwoven network. Due to these advantages, the mass loading of sulfur was increased up to 5 mg cm −2 while maintaining a high initial specific capacity of 1400 mAh g −1 and stable cyclability.

The development of electric vehicles and portable devices require high power and high energy density batteries. In this regard, among the existing energy storage systems, the lithium-ion batteries (LIBs) play a key role. However, the energy and power densities of conventional LIBs are reaching the limited theoretical values and cannot fulfill requirements for new generation portable devices and electric vehicles. Sulfur is a promising replacement for intercalated cathode materials, since it has high theoretical capacity of 1672 mAh g-1 and high gravimetric energy density of 2600 Wh kg-1.1 Moreover sulfur has several advantages such as low cost, environmental friendliness and abundance.2 However, commercialization of lithium-sulfur batteries faces several difficulties related to low conductivity of sulfur, polysulfide dissolution and lithium dendrite growth.3,4 The aim of this research was to increase mass loading of sulfur in the electrode, which in turn requires improvement in the bulk conductivity. For that reason, high sulfur loading S/DPAN/CNT composite cathode was prepared by a simple and efficient way of designing micro and nano level 3D carbon networks. The covalent bonding between pyrolyzed PAN and sulfur diminishes polysulfide dissolution, while CNT maintains structural integrity, acting as nanoscale interwoven skeleton and ensures electron transfer within and between S/DPAN granules.5 Then S/DPAN/CNT was impregnated into pores of commercial carbon fiber paper (CFP), which in its turn provides bulk electron conductivity in macro level. As a result, mass loading of sulfur was increased up to 5 mg cm-2while maintaining a high initial specific capacity of 1400 mAh g-1 and stable cyclability. Acknowledgements This research was supported by the targeted state program BR05236524 “Innovative Materials and Systems for Energy Conversion and Storage” from the Ministry of Education and Science of the Republic of Kazakhstan for 2018-2020. References: [1] K.H. Shin, K.-B. Kim, C.S. Jin, W. Ahn, K.N. Jung, J. Power Sources 202 (2011) 394–399. [2] Y. Zhang, Y. Zhao, T. N. L. Doan, A. Konarov, D. Gosselink, H. G. Soboleski, P. Chen, Solid State Ionics 238 (2013) 30–35. [3] M. Li, R. Carter, A. Douglas, L. Oakes, C. L. Pint, ACS Nano 11 (2017) 4877–4884. [4] Z. Nie, J.-G. Zhang, N. D. Browning, Q. Li, L. B. Mehdi, X. Xie, J. Liu, G. L. Graff, J. Zheng, S. Ferrara, Adv. Energy Mater. 5 (2015) 1402290.

Three-dimensional materials can improve the performance of energy storage systems by providing large active surface. Thus, the research was focused on designing a full 3D battery based on electrodeposited Ni3Sn4 (Ni-Sn) anode and polymer gel electrolyte/separator that was coated via layer-by-layer (LbL) technique. Advantages of the LbL approach was appliance of polymer material onto a rough surface of 3D structured electrode material, and thickness control of the coated gel polymer electrolyte. The structure of deposited electrode material was confirmed by XRD. The thickness estimation of coated layers, and cross-section view of 3D battery were depicted via SEM. Electrochemical activity of Ni-Sn alloy with LbL coated gel electrolyte demonstrated redox couples for lithiation and delithiation processes. LbL technique proved that polymer can be coated uniformly onto 3D structure electrode and function as the electrolyte and separator. Acknowledgement This research was supported by the research grants #091019CRP2114 “Three-dimensional all solid state rechargeable batteries” from Nazarbayev University.