Development of LMR-NMC Based Cathodes and Si-Based Anodes for High Energy Density Lithium-Ion Batteries

I would also like to thank the head, the Department of Chemistry and all other colleagues of the Department for their direct/indirect support in my research work. I am also very grateful to the non-teaching staff of the Department of Chemistry.

Chapter 4: Synergistic Effect of Magnesium and Fluorine Doping on the Electrochemical Performance of LMR-NMC Cathodes

Chapter 6: Binder and Conductive Additive Free Silicon Electrode Architectures for Advanced Lithium-Ion Batteries 159

In-situ 3D Electrode Fabrication of High Capacity Silicon- Carbon Anodes for Lithium-Ion Batteries 175

Nomenclatures

Definitions

Power density: The ratio of the available power from a battery to its weight (W kg-. 1) or volume (W L-1). State-of-charge: The ratio of capacity available at that moment to the total available capacity.

Introduction to Lithium-Ion Batteries

Abstract

Importance of Energy Storage

Among the leading secondary battery systems: lead-acid batteries, Ni-based batteries and LIBs, the LIBs rise faster due to high energy density (150-200 Wh kg-1 versus 30 Wh kg-1 for lead-acid and 50-80 Wh kg-1 for the Ni-based batteries) and long cycle life [9, 10]. Due to high energy density, LIBs are the choice to power mobile phones, portable computers, camcorders, power tools and even in hybrid electric vehicles and electric vehicles [11-15].

Lithium-Ion Battery: Significance and Historic Outlook

The battery showed 30% more capacity per volume compared to conventional LIBs that contained LCO as cathode and graphite as anode. Subsequently, in 2007, A123 Systems of USA developed LIB consisting of LiFePO4 (LFP) as cathode and graphite as anode, which showed improved current capacity, high thermal stability, stable cyclability, long battery life with minimized cost used for hybrid electric vehicles and grids.

Working principle of LIB

During charging, Li-ions are extracted from the cathode and inserted into the anode, and while discharging, the reverse occurs, where electrons move through the external circuit providing the energy. The half-cell reactions occurring at the cathode and anode during the charge-discharge cycles of a lithium-ion cell are presented as follows.

Electrochemical Constituents of a Lithium-Ion Cell

Layered, spinel oxides and olivine cathodes

LiCoO 2 and its derivatives
LiMnO 2
LiMn 2 O 4
LiMn 1.5 Ni 0.5 O 4 (NMS)
Olivines
Future cathodes for LIB

Anodes

Lithium anode
Carbon based anodes
Tin (Sn) based anodes
Titanium oxide
Lithium Titanium Oxide (LTO)
Silicon

Electrolytes

This is because the ion exchange process has a large influence on the defect chemistry of the host structure, which in turn affects the electrochemical performance of LMOs. In order to improve the performance of anatase material, several strategies have been used, such as the synthesis of nano-sized particles.

Fig. 1.2: Layered structure of LiMO 2 (M = Co, Ni, Mn, Fe) (Adopted from Ref. [52])

Drawbacks and Failure Modes of Lithium-Ion Batteries

The present study

From the above literature review on cathode, anode materials for lithium-ion batteries (Chapter 1), it is clear that next-generation LIBs can have twice the energy and power density of currently available LIBs with reduced cost and improved safety. With this background, Chapter 2 of the thesis is an attempt to evaluate the energy and power density of currently available LIBs with respect to C-rate and temperature.

Fig. 1.8: Thermal runaway in a lithium-ion battery (Adopted from Ref. [329])

Chapter 3 describes an effort to improve capacity retention, C rate performance and energy density of LMR-NMC by 3D electrode architecture and LiF

Moreover, for the optimal performance of LIBs operating at low temperatures, low C rate application is most preferable. The voltage decay which is the main problem of LMR-NMC is minimized in Mg-F doped LMR-NMC compared to pristine LMR-NMC.

Chapter 5 describes another approach of improving energy density, C rate performance of LMR-NMC material by blending with carbon coated LiMnPO 4

Together these substitutions increase the specific energy density and energy per unit area of the electrode. Full cells based on LMR-NMC cathodes and free-standing Si-C composite electrodes yield an energy density of 530 Wh kg-1, which is almost twice the energy density of currently available LIBs.

Wan, Preparation and characterization of high-density spherical LiCoO2 cathode materials for lithium-ion batteries, J. Zhang, Synthesis and electrochemical properties of K-doped LiFePO4/C composite as cathode materials for lithium-ion batteries, Journal of Solid State Electrochemistry. Si, Sr-doped Li4Ti5O12 as the anode material for lithium-ion batteries, Solid State Ionics.

Zhao, Preparation and electrochemical performance of La 3+ and F-co-doped Li4Ti5O12 anode material for lithium-ion batteries, J.

Effect of Temperature and C rate on

Ragone Plots” of Lithium-Ion Batteries

Abstract
Experimental

Structural and physical characterizations of electrode materials
Electrochemical characterizations

Results and Discussion

Electrode materials characterization
Isothermal discharge profiles
Galvanostatic discharge profiles
Ragone plots and Power-Energy Index (PEI)

Conclusions

The ragon plot of lithium ion cells discharged at different rates and temperatures C is shown in Fig. The low efficiency of lithium ion cells at low temperatures is due to the reduction of electrolyte conductivity and lithium ion diffusivity. Discharge temperature and C-rate have great influence on the performance of lithium graphite/LCO-ion battery.

Yoshiyasu, Effect of Addition of Conductive Material on Positive Temperature Coefficient Cathodes of Lithium-Ion Batteries, J.

Fig. 2.1: Photograph of 700 mAh lithium ion cells used for electrochemical testing at different C rates and different temperatures

Study of High Energy Density Li-Mn Rich (LMR) Ni-Mn-Co Oxide (NMC)

Abstract

The study opens up a possibility for LMR-NMC cathode material which has almost twice the capacity of currently used cathode and could be a potential replacement cathode for LIBs used in electric vehicles.

Background and Motivation

And solid electrolyte coating such as LiPON improved the capacity retention and scale performance of LMR-NMC [33]. LMR-NMC suffers from poor cyclability (capacity retention), rate capability due to the low electronic conductivity of LMR-NMC and the deposition of a thick SEI layer formed by a reaction of the cathode surface with organic electrolytes in cycles of high voltage (>4.4 V) [46]. Partially O2- is replaced by F- on the surface of LMR-NMC and due to which the average oxidation state of the surface metal ions is decreased, which leads to the reduction of the charge potential thus minimizing the decomposition of the electrolyte and providing better performance good electrochemical.

There are similar reports that LaF3 and AlF3 coatings also improve the electrochemical performance of LiMn2O4 and NMC, respectively [54-55].

Experimental

Synthesis of LMR-NMC and F-LMR-NMC
Structural and physical characterization of LMR-NMC and F-LMR- NMC
Electrode preparation and cell assembly
Electrochemical characterizations of LMR-NMC and F-LMR-NMC The electrochemical performance of the LMR-NMC and F-LMR-NMC

A few minutes after the material is kept in the oven at 400 oC, self-ignition occurs, forming amorphous LMR-NMC. For comparison, pristine LMR-NMC (no LiF coatings) was prepared from amorphous LMR-NMC by annealing at 800 oC in an alumina crucible for 20 h in air. The powder XRD measurements on LMR-NMC and doped LMR-NMC were performed using an X'Pert Pro diffractometer (Holland) (reflection geometry, Cu Kα radiation, receiving slit of 0.2 mm, scintillation counter, 30 mA, 40 kV) .

The cells are assembled using composite electrodes comprising LMR-NMC, F-LMR-NMC powder as active masses, Li foils as counter and reference electrodes, and polyethylene-polypropylene three-layer separator (Celgard, Inc., Canada).

Results and Discussion 1. Structural characterization

Physical characterizations and compositional analyses
Electrochemical performance studies

Structural, physical, electrochemical assessment of carbon fibers
Electrochemical assessment of LMR and F-LMR-NMC

Table.3.1: Comparison of lattice parameter values of pristine material and different proportions of LiF and LMR-NMC material. HR-SEM and HR-TEM images in both pristine LMR-NMC and F-LMR-NMC materials converge. Both pristine LMR-NMC and F-LMR-NMC on CF show good cycling stability as shown in Fig.

Therefore, in this work we focus on the electrochemical studies of the pristine and F-LMR-NMC only CF current collector.

Fig. 3.1: XRD patterns of: (a) pristine LMR-NMC, (b) F-LMR-NMC (1:100 wt. %), (c) F-LMR- F-LMR-NMC(1:75 wt

Conclusions

Li, Recent advances in Li-rich layered oxides as cathode materials for Li-ion batteries. Liang, Improved electrochemical properties of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 with ZrF4 surface modification as cathode for Li-ion batteries, J. Yang, The effects of TiO2 coating on the electrochemical performance of Li[Li0.2Mn0 .54Ni0.13Co0.13]O2 cathode material for lithium-ion battery, Solid State Ionics.

Suna, Improvement of high voltage cycling behavior of surface modified Li[Ni1/3Co1/3Mn1/3]O2 cathodes by fluorine substitution for Li-Ion batteries, J.

Synergistic Effect of Magnesium and Fluorine Doping on the Electrochemical

Abstract
Experimental

Synthesis of LMR-NMC and Mg-F doped -LMR-NMC
Structural, physical and electrochemical characterization of LMR- NMC and F-LMR NMC

Structure and morphology
Electrochemical performance

Conclusions

Layered LMR-NMC cathodes are attractive cathodes for powering electric vehicles (EV) due to their high energy density (>1000 Wh kg-1). Mg-doped LMR-NMC is synthesized by combustion method by taking stoichiometric amounts of Li(NO3) (1.2 mol), Mn(NO3)2. The XRD pattern of the pristine and Mg-F doped LMR-NMC samples is shown in Fig.

The LMR-NMC composite cathodes show a significant voltage drop compared to the doped LMR-NMC sample (Fig. 4.5 (a) and (b), Fig.

Fig. 4.1: XRD patterns of: (a) pristine LMR-NMC, (b) Mg(0.02)-F-LMR-NMC (c) Mg (0.05)-F- (0.05)-F-LMR-NMC, and (d) Mg (0.08)-F-LMR-NMC synthesized by solution combustion method followed by LiF coating on to LMR-NMC by solid state synthesis at 800

Blended Electrodes for High Performance Lithium-Ion Batteries

Abstract
Background and Motivation
Experimental

Synthesis of C-coated LiMnPO 4 nanoparticles
Synthesis of LMR-NMC and blended cathode materials
Structural, physical and electrochemical characterization of LMR- NMC, LMP and blended materials
Ageing test LMR-NMC, LMP and blended materials

Structural, physical characterization of LMR-NMC, LMP and blended materials
Electrochemical performance studies of LMR-NMC, LMP and blended materials
Mn dissolution studies of LMR-NMC, LMP and blended materials Dissolution of Mn is the major cause of capacity fade and structural transformation
Discussions

Conclusions

Since the operating voltage of C-LMP matches that of LMR-NMC, C-LMP is an ideal to mix with LMR-NMC. 5.3: (a) 1st charge voltage profiles, (b) 5th discharge voltage profiles (maximum capacity obtained) pristine LMR-NMC, pristine C-LMP and mixture of LMR-NMC and C -LMP as shown in the figure. Fig.5.5: Cycle life of: (a) LMR-NMC, mixed LMR-NMC and C-LMP, (b) C-rate performance of mixed electrode, (c) Comparison of rate capability of LMR-NMC and mixed electrode.

Improvement in energy density of the mixed material is due to high flat plateau voltage, stable capacity and stable crystal system of C-LMP and high capacity of LMR-NMC.

Fig. 5.1: XRD patterns for: (a) LMR-NMC and (b) C-LiMnPO 4

Binder and Conductive Additive Free Silicon Electrode Architectures for

Abstract
Experimental

Synthesis of Si-NPs by magnesiothermic reduction
Post-mortem TEM analyses

Structural, physical characterization of Si-NPs
Discussions

Conclusions

6.1: (a) X-ray diffraction pattern of as-synthesized Si-NPs by magnesiothermal reduction from fumed silica; (b) Raman spectra of the as-synthesized Si-NPs. 6.2: (a) SEM image of the as-synthesized Si-NPs showing small particle sizes; (b) SEM image of the as-prepared Si-NPs on copper current collector. These Si-NPs cycle more than 500 cycles due to good electrical contact of Si-NPs with current collector.

The as-prepared Si-NPs pressure embodied on the copper foil current collector overcomes the problems of silicon anodes in versatile ways.

Fig. 6.1: (a) X-ray diffraction pattern of as-synthesized Si-NPs by magnesiothermic reduction from fumed silica; (b) Raman spectra of the as-synthesized Si-NPs

In-situ 3D Electrode Fabrication of High Capacity Silicon-Carbon Anodes

Abstract

Binder- and additive-free porous nickel-based 3D current collector, conformally coated with layers of silicon, delivers a high capacity of 1650 mAh g-1 after 120 charge/discharge cycles [42]. Here we present a unique organic binder-free, additive-free 3D electrode architecture of Si-C NPs on CF current collector that replaces the conventional copper foil current collector [50–51]. CF mat has numerous advantages over a copper current collector, such as the integration of a large amount of active material into the 3D CF network and ensures high interfacial contact of active material with the conductive network.

Thus, an annealing mixture of P-pitch and Si-NPs coated on a CF current collector at high temperatures ≥ 500 oC melts the P-pitch and enables a conformal coating throughout the silicon and carbon fibers, allowing a conductive network and enough room for volume expansion and contraction without pulverizing.

Experimental

Synthesis of Si-NPs and structural-physical characterizations
Structural-physical characterizations carbon fibers, carbonized pitch and electrodes
Electrode preparation and cell assembly
Electrochemical performance studies

In addition, the bond strength of carbonized pitch with silicon and carbon fiber is affected by temperature. Electrodes developed by this method provide enough space for silicon surrounded by carbonized pitch on carbon fiber that supports the volume expansion and contraction during cycling, thus reducing the pulverization of the silicon. 7.1: (a) Foamy structure of P-stitch at temperature of ≥ 700 oC, and b) Electrode structure of Si-NPs with P-stitch on CF current collector at 700 oC.

The electrochemical performance of the samples comprising pristine Si-NPs, on copper foil (conventional electrode) and only pitch-coated carbon fiber and finally silicon-carbon composite on carbon fiber as active masses were measured using Solartran Cell Test system and Arbin battery cyclers as explained in chapter 6.

CF mats having diameter in the range between 5-10 µm as shown in Chapter 3, Fig.

Results and Discussion

Structural-physical properties of Si-NPs, Si-C composite electrodes

Complete cells are assembled using Mg-F doped LMR-NMC composite cathodes as developed in Chapter 4 and current Si-C composite anodes. Impedance measurements were performed in a frequency range between 1 MHz and 10 mHz before cycling in the open circuit condition (OCV) and in the fully loaded condition after 100 cycles. Charge-discharge cycling was performed in the potential range between 1.2 V and 50 mV using constant current.

Whole cells of the LMR-NMC cathode and Si anode were cycled in the potential range between 2.0 V and 4.6 V.