In this study, we found that the selective chemical etching method using PVP and AgNO3 is very promising to obtain significantly improved electrochemical performance of cathode materials even at high voltages. Furthermore, we found that co-modification of multilayer LiCoO2 with a nanometer-scale Co3O4 overlayer by chemical etching minimized the performance loss and maximized the cathode rate performance without loss of electrode density. Furthermore, since the fabrication of the copper substrate for nanopillars involves only conventional top-down processes, nanopillars can be created in a simple and rapid process by surface control and simple modulation of nanopillar density or diameter.
Stationary Electric Energy Storage – Battery
Introduction: The need of electric energy storage system
Battery for EES applications
- Lead-acid battery
- Na-S battery
- Li-ion battery
- Redox flow battery: All-vanadium
Recent progress in battery for EES applications
- Metal-Air battery: Zn-Air
- Advanced redox flow battery
- Aqueous lithium flow battery
- Waste-Li-liquid flow battery
Conclusion
The Details in Li-ion Batteries
Li-ion Batteries’ trend in 2014
- Electric vehicles
- Energy storage system
For a cell configuration, the laminate type was developed for use in practical applications due to its high thermal stability and capacity with low internal resistance.6 The electromotive force of LIB is ~3 times higher than that of Ni-based rechargeable batteries such as nickel-metal hydride (NiMH ) system (Table 1).7 Currently, the cost of cathode material accounts for 30-40% of LIB production, as shown in Figure 1a,8 and their specific capacity is approximately 150 mAh/g in the current system . In other words, the supply of environmentally friendly vehicles such as electric vehicles can be an urgent task due to the mileage limitation in the gasoline system. If there are time and space limitations for battery charging, EV estimates for customers may be devalued.
According to the DOE report on battery production, production costs can also be efficiently reduced to 30-40% if annual battery production is increased from 10,000 to 100,000 units.19 In reality, because part of battery costs is 30~40% Battery Suppliers , which represent 40% of the total electric vehicle price, must have a certain level of economic scale to reduce the overall battery cost, including a ready supply of electrode materials and good economic feasibility. The representative field of ESS that LIB adapts will be uninterruptible power supply (UPS) which has formed a $10 billion market,24 due to LIB's cost competitiveness. The price of a lead-acid battery is $300/kWh, which is 40% higher than $500/kWh from LIB.11 However, if we consider the price per 1 kW, assuming that its value corresponds to the maintenance of the UPS system for 30 minutes, then Battery requires $360/kW, but LIB costs $263/kW.24 LIB in turn can be sufficiently considered in the existing UPS market due to its 27% cost savings.
In addition, the LIB weight per capacity is 1/3 that of a lead-acid battery, and LIB can be 1/5 lighter than that of lead-acid batteries, with a space saving of 1/3.24 Finally, due to the long lifespan of LIB (10 years) compared with lead-acid batteries (5 years), lead-acid batteries in UPS can be replaced by LIB, which will make the exchange rate faster than expected. Currently, only LIB can be applicable to both conditions, and the market prospects of ESS equipped with LIB can be positively expected to increase due to the low limitation of capacity design and installation. Also, the effect of cost savings can be expected, as LIB can be efficiently adapted in ESS via the technologies currently used in IT and EV applications.
Therefore, the demand for LIBs will increase exponentially because it is recognized as an essential energy storage in ESS.
Materials in Li-ion batteries
- Cathode
- Anode
- Separator
- Electrolyte
- Current collector
Also, not only can it be operated at ~4V with high power density caused by the 3-dimensional Li-ion path, but also LMO is cost competitive due to the low price of Mn. Despite these advantages, it has a drawback of capacity reduction at high temperatures.26, 29 In the structure of olivine, LFP is a representative and has been attractive due to its low cost, high thermal stability and environmental friendliness. 30 LFP excellently describes the electrochemical properties due to a unique stability of the structure. Recently, carbon coating and Mn addition to the LFP structure have been attempted to increase an electrical conductivity and discharge voltage, respectively. 31-32 Depending on the characteristics of the cathode materials, LCO and NCA are mainly applicable to small IT equipment and electric-car tools, respectively, while NCM and LMO have been used in ESS or EV applications.
Consequently, alloys such as silicon, germanium, and tin have been proposed, but are difficult to cycle due to the desorption phenomenon caused by volume expansion/contraction during cycling. In addition to the mentioned anode materials, currently studied is Li4Ti5O12 (LTO) with an operating voltage of 1.5 V, which shows little electrolyte degradation. In combination with a 5 V cathode electrode, studies based on 3 V cells have been carried out to achieve high power and energy density.34 In the case of metal oxide, it has high cycling stability and power density, but it is difficult to commercialize due to low electrical conductivity and large initial irreversible capacity.
Depending on how the separator is produced, it can be classified into dry-based and wet-based processes.17 IT equipment adapts a separator from a mixed process, while the EV system uses it from the dry process due to a stability of excellent at high temperature. The electrolyte can be considered as an intermediary that allows the transport of lithium ions during charging/discharging. It consists of a co-solvent, which is mixed with a low-viscosity solvent and a high-permeability solvent, and a lithium salt prepared by dissolving a predetermined concentration.38 Lithium hexafluorophosphate (LiPF6) is generally used as lithium salt due to high ionic conductivity and good stability. To stabilize an interface between the electrode and the electrolyte, additives are added, and currently a fluorine-based electrolyte is being used to improve the stability of the electrolyte with poor flame retardancy.39 For the development of advanced electrolyte, it is strongly considered that the electrolyte should be designed with i) non-fluorine-based flame retardant properties, ii) electrochemical stability within the working voltage, iii) thermal stability at high operating temperature and iv) ensuring ion conductivity at low temperature.
In addition, a polymer electrolyte is considered due to small leakage and high stability, but its ionic conductivity is low.
The properties changes at high temperature and voltage in LIB
Introduction
Currently, a dominant cathode material of Li-ion battery for 3/4G smart mobile phones is surprisingly LiCoO2 due to high capacity, low self-discharge, excellent cycle life and high energy density (3 Wh/cc).1-2 LiCoO2 has the hexagonal α-NaFeO2 -phase consisting of the layered rock salt structure of the order of magnitude Li+ and Co3+ on alternating (111) planes in cubic structure.3-5 However, its main disadvantages are rapid capacity degradation at higher speeds and rapid capacity fade above 4.4V (compared to lithium metal). It has been suggested that the phase change at ∼4.5V is sufficiently large to cause mechanical stresses among the grains. This electrochemical grinding combined with Co4+ dissolution and structural degradation by lithiation/delithiation results in capacity loss.7-9 To minimize Co4+ dissolution, the metal oxides, such as ZrO2,10 TiO2,10 B2O3,10 Al2O3,6, 10-12 MgO, 11 SnO2 , 11 ZnO, 13 and AlPO414 have been investigated.
These types of metal oxides play a key role as protective layers to prevent a direct interaction between the electrolyte solution and LiCoO2, resulting in reducing the cobalt solution above 4.3 V during cycling.7, 15-16. In this regard, LiCoO2 with different morphologies such as 1D, 2D, and 3D can also be considered to improve its rate performance, due to sufficient contact area between electrolyte and active materials.17 However, their electrochemical performance was not noticeably improved. Here, we report for the first time the simultaneous modification of the pristine to the layered 3D-LiCoO2 with a nanoscale Co3O4 coating layer by chemical etching to minimize the capacity loss and to maximize the rate capability of the cathode without loss of the electrode density.
Experimental section
- The layered 3D-LiCoO 2 preparation
- Analysis instrument
- Coin-cell preparation
Results and discussion
Etched Graphite with Internally Grown Si Nanowires from Pores as an Anode for
- The preparation of Si nanowires embedded in porous graphite
- Fabrication of lithium ion half-cell
- Fabrication of a-Si/3D-Cu electrode
- Fabrication of the Li-ion half-cell
- Electrochemical characterization of the half-cell
- Morphology characterization of the a-Si/3D-Cu nanopillar electrode
Cross-sectional SEM images of (a) bare MCMB and (b) etched MCMB and low-magnification SEM images of (c) bare graphite, (d) charged polystyrene-b-poly(2-vinylpyridine) micelles bearing Ni- ion on graphite surface, (e) porous graphite after hydrogenation at 1000 ˚C for 1 h, and (f and g) Si nanowires grown from porous graphite after catalyst exchange from Ni to Au, followed by VLS process with SiH4 at 550 ˚C for 30 min (g is enlarged image of (f)) ……….96 Figure S2. The peak positions corresponding to graphite (green), SiC (pink) and Ni2Si (blue) are shown ………97 Figure S3. a and b) SEM images of Si nanowires from the pores in the controlled experiment with SiH4. SEM images of the fabricated (a) blanket film, (b) a-Si/3D-Cu electrode with 250 nm diameter nanopillars, and (c) a-Si/3DCu electrode with 500 nm diameter nanopillars, and (d, e, and f) the blanket film and a-Si/3D-Cu electrodes with 250 and 500 nm diameter nanopillars, respectively, after 100 cycles (inset: top view).
Lithium reaction mechanism and high rate capability of VS 4 -graphene
Synthesis of VS 4 -rGO composites
After preparing a homogeneous solution, the mixture was transferred to a 500 ml Teflon-lined stainless steel autoclave, tightly sealed, and a hydrothermal reaction was carried out at 160 °C for 24 h. Furthermore, only rGO was obtained via the hydrothermal reaction of the GO solution under the same conditions but without the addition of Na3VO4 and C2H5NS. For synthesis of the reference VS4–10 wt% CNT composite sample, refer to the Supporting Information.
Characterization of the materials
Electrochemical characterization of the materials
All three charge profiles appear to be similar and two potential plateaus at ~1.8 V and ~2.4 V are observed. The clear difference between the CV and voltage profiles of the first and second discharge processes indicated an irreversible phase transition during the first discharge-charge process. TEM and EDS mapping were used to analyze the fully discharged and charged VS4-rGO electrodes for better understanding the mechanism of lithium storage.
The internal electronic conductivity of the cells can be improved due to the generation of vanadium metal during cycling. The electrochemical impedance of the VS4-rGO-based coin-type lithium cell was measured before and after cycling (Figure 4A). Electrochemical performance is highly related to the distribution of active materials in the electron-conducting matrix.
First, the existence of rGO improved both the conductivity and stability of the VS4-rGO electrode, which may cause a better cycle stability and rate capability. V improved the electronic conductivity of the Li2S–V or S–V composite during the following discharge–charge process. In addition, the dissolution of polysulfide, which is common in Li-sulfur batteries, may be suppressed due to the absorption effect of the nano-sized V with high surface energy.
The carbon content of the produced VS4-CNT composite was 10 wt% according to elemental analysis.
