Studies Of Ni-Mn And Co-Mn Oxides As Cathode Materials For Aqueous Batteries And 3D Lithium Anodes For Lithium Batteries

With the rapid development of modern society,there is an increasing dependence on secondary battery systems.And based on the refined functional classification of the society,the secondary batteries should meet different requirements for various applications.On one hand,the safety,long-term stability and cost are the most important criteria for large-scalable intermittent static energy storage system.Aqueous battery systems are considered to be one of the ideal choices to satisfy the above requirement,due to its high safety,low cost,eco-friendness,high ionic conductivity of aqueous electrolyte and easy realization of large-scalable manufacturing.The performance of aqueous batteries is dependent on the host materials.Hence,the development of the suitable host materials for aqueous batteries becomes a hot topic during recent years.On the other hand,the working endurance of portable electronic devices?such as cell phones,electric vehicles?mostly relies on the energy storage capability of secondary batteries.So the energy density becomes the most valuable criterion for these secondary batteries.The Li metal anode is the ultimate anode material for high-energy batteries due to its highest theoretical capacity(3860 mAh·g^-1),lowest redox potential?-3.04 V vs.SHE?and lightest density(0.59 g·cm^-3).However,the severe Li dendritic growth and infinite volume change during cycling are the two main issues that hinder its practical application.In this paper,in the first part,various synthesize methods for binary transition oxides cathode materials in aqueous capacitor battery system are developed;and the insertion/extraction behaviors of Na⁺,Mg²⁺and Zn²⁺in the binary oxides are investigated;the influence of anion or poly anion groups SO₄^2-?NO₃^-?Cl^-on charge/discharge performance is also studied.In the second part,two types of 3D carbon structure integrated with Li metal as anode materials are synthesized to solve the serious problems of Li metal anodes for high-energy Li batteries in organic electrolyte;and the reason for enhancement on long-term cycling stability of Li metal anodes by 3D structure design are also explored.The main contents are as follows:Material P2-Na_2/3Ni_1/3Mn_2/3O₂ is synthesized by co-precipitation method.From the scanning electron microscope,the as-prepared material is constructed by two-dimensional?2D?ultrathin nanosheets that the size is ranging from 0.8¹.6?m.The material was investigated,for the first time,as the cathode material for an aqueous Na-ion capacitor battery.The Na_2/3Ni_1/3Mn_2/3O₂ electrode is charged between-0.8¹.0 V?vs.SCE?in 1 mol L^-1 Na₂SO₄with no water decomposition.The reversible capacity of the electrode reached 157 mAh·g^-1 at0.05 C and retained to be 84 mAh·g^-1 and 51 mAh·g^-1 at 0.20 C and 0.50 C,respectively.After 80 cycles at 0.20 C,the specific capacity of Na_2/3Ni_1/3Mn_2/3O₂ remains to be 42 mAh·g^-1.Nano-sized M_1/3Ni_1/3Mn_2/3O₂?M=Mg or Zn?is synthesized from Na_2/3Ni_1/3Mn_2/3O₂ via an electrochemical conversion method.XRD patterns reveal that crystal structure is maintained after the reversible Mg²⁺or Zn²⁺intercalation/deintercalation.Its performance for Mg²⁺and Zn²⁺intercalation/deintercalation in aquesous electrolytes is evaluated by cyclic voltammetry,galvanostatic cycling and electrochemical impedance spectroscopy.Mg_1/3Ni_1/3Mn_2/3O₂exhibits an initial capacity of 170.5 mAh·g^-1 in 1 mol·L^-1 Mg?NO₃?₂,Zn_1/3Ni_1/3Mn_2/3O₂displays an initial discharge capacity of 113.7 mAh·g^-1 in 1 mol·L^-1 ZnSO₄.P2-Na_2/3Co_2/3Mn_1/3O₂ is sucessfully synthesize via a hydrothermal method.Mg_1/3Co_2/3Mn_1/3O₂ is synthesized from P2-Na_2/3Ni_1/3Mn_2/3O₂ via an electrochemical conversion method.The XRD patterns of samples under different calcination temperature indicates that P2-Na_2/3Co_2/3Mn_1/3O₂ is the pure phase without impurities and has a good crystallinity after calcination under 880°C.The scanning electron microscope images show that the as-prepared material has a lamination morphology with micron-sized ultrathin layers whose size is 1⁵?m.The insertion/extraction behavior of Na⁺and Mg²⁺in the[Co_2/3Mn_1/3O₂]slabs is investigated by cyclic voltammetry,galvanostatic cycling and electrochemical impedance spectroscopy.P2-Na_2/3Co_2/3Mn_1/3O₂ electrodes deliver a discharge capacity of 81.1,41.6 and 32.9 mAh·g^-1 at 20,50 and 100 mA·g^-1,respectively;the ionic diffusion coefficient D⁺_Na is 8.5×10^-12 cm²?s^-1.Since the ionic radius of Mg²⁺is smaller than that of Na⁺,Mg²⁺has better electrochemical insertion/extraction performance in the[Co2/3Mn1/3O2]slabs.Mg_1/3Co_2/3Mn_1/3O₂ electrodes deliver a discharge capacity of 96.4,81.1,69.1 mAh·g^-1 at 20,50,100 mA·g^-1,respectively;D_Mg²⁺value is as high as 1.0×10^-9 cm²?s^-1.The Al2O3 coated carbon nanotube sponge?CNTS??ALD-CNTS?composite is synthesized by growing a Al2O3 nano-layer on carbon surface of three-dimensional?3D?CNTS substrate via atomic layer deposition?ALD?.The Coulombic efficiency of current collectors of ALD-CNTS and Cu are 92.4%?80 cycles?and 40.2%?50 cycles?at 1 mA·cm^-2,which is tested by galvanostatic charge/discharge.The electrodes Li@ALD-CNTS and Li@Cu are prepared by electrochemical depositing 10 mAh·cm^-2 of Li.The cycling performance demonstrates that Li@ALD-CNTS electrode delievers an overpotential of 30mV after 100 h cycling while Li@Cu electrode shows an overpotential of 380 mV after 66 h cycling.The scanning electron microscope images show that no obvious Li dendrites on the Li@ALD-CNTS electrodes after cycling;in sharp comparison,Li@Cu electrode shows a severe dendritic morphology after cycling.The good cycling stability of Li@ALD-CNTS electrode indicates that the Li dendritic growth can be effectively alleviated by 3D carbon structure;An additional conformal Al2O3 layer on the CNT sponge coated by atomic layer deposition?ALD?further affords a robust interfacial protection of the Li metal due to its good chemical stability and high mechanical strength.A carbonized wood?C-wood?is proposed as a three-dimensional?3D?,highly porous?73%porosity?conductive framework with well aligned channels to host Li.Molten Li metal can infuse into the straight channels of C-wood to form a Li/C-wood electrode.The scanning electron microscope images shows the morphology change of C-wood before/after Li infusion,indicates that Li is successfully infused into the aligned pores of C-wood due to the wetting improvement between carbon/Li interface after ZnO coating.The Li/C-wood electrode can deliever a discharge capacity of 2650 mAh·g^-1 by setting a voltage cutoff of 1 V for the galvanostatic discharge test.The cycling stability of Li/C-wood symmetric cells and bare Li symmetric cells are evaluated by galvanostatic charge/discharge.The as-prepared Li/C-wood electrode presents a lower overpotential of 53 mV after 165 cycles at 1 mA·cm^-2;while bare Li metal electrodes shows an overpotential of 0 mV after 165 cycles,indicative cell inner short-circuit by Li dendritic growth.The result reveals that the C-wood channels function as excellent guides in which the Li stripping/plating process can take place and effectively confine the volume change that occurs.Moreover,the local current density can be minimized due to the 3D C-wood framework,leading to a good inhibition of Li dendrites.