GRAPHENE-BASED LITHIUM-ION BATTERY ENERGY STORAGE

SYSTEMS

Jesca R. BenitezBS-Electronics and Communications Engineering

Pala-o, Iligan City, Philippinesjescabenitez@yahoo.com

Abstract—This paper investigates on graphene-based battery for anode and cathode material and results will be summarized as well as its improvements in applications. Various approaches to different types of graphene as nanocomposites and the process of preparing the anode or cathode for the lithium-ion batteries as well as their electrical, chemical and mechanical properties are discussed.

I. Introduction

The ever-increasing demand on energy has driven many countries to invest heavily in finding new sources of energy. Investigations and innovations have been taking place to be able to come up with efficient devices that stores energy. One of which is the lithium ion batteries. This kind of battery has many unique advantages compared to those conventional batteries. These merits include high open-circuit voltage, high energy density, long useful life, no memory effect, no pollution and low self-discharge rate. Because of these advantageous properties of lithium ion batteries, it made them quickly become the new generation of secondary batteries in recent years and, these are used in mobile phones, laptops as well as portable devices.

In this report, we will determine the feasibility of Graphene -based lithium ion battery and analyze its economical effect when used in energy storage system and its applications. Investigations on graphene-based battery for anode and cathode material will be summarized as well as its improvements in applications.

1.1 Applications

The applications of battery energy storage systems are basically divided into five categories namely: electricity supply, ancillary service, grid systems, renewable integrations and utility customers or end users.

Ralph F. GamilBS-Electronics and Communications Engineering

Tibanga, Iligan City, Philippinesralph.gamil@gmail.com

Electricity Supply

When the main source of energy is low, it is practical to use ‘Time-Shifting of Energy Delivery’ where the main source of power is turned off temporarily for a period of time and energy storage systems take over. This method may also be used to reduce cost during periods of low demands. Also, for contingencies or emergencies such as exhaustion of the generator unit, the battery energy storage system compensates for such failure to raise back the capacity supply credit to norm. In other words, BESS acts as a secondary power source where it limits the use of diesel or generator.

Ancillary Service

In this category, the battery energy storage system continuously monitors the system with respect to its voltage, current, and frequency. If any significant fluctuations or deviations are found, the storage system immediately responds and supplies sufficient power until the fault is fixed. Basically, it provides necessary support for the primary operating system.

Specifically, for power quality and reliability, it maintains voltage and frequency within its safe operating ranges. Moreover, it controls regulation by maintaining the balance between the generation and load.

Grid Systems

In this category, the battery storage system also provides grid operational support mainly by serving as a back-up source of energy due to unstable sources and transmission support. Also it uses time-shifting and regulation control for stability of grid systems.

Renewable Integration

Renewables are naturally unsteady or not continuous. So the storage system provides automatic power support to prevent the generator from failing below the safe levels.

Moreover, due to the instability of the renewable energy storage, BESS suppresses fluctuations of parameters such as voltage, current and frequency by smoothing the very short-term variations.

This is an illustration of fluctuations in load versus time. The goal here is to make it as horizontal as possible which indicates stability and balance.

Utility Customers

In markets where the demand for electricity exceeds the available power generation capacity, utilities need to consider the practicalities of load management and load shedding during peak demand times of the day. With the aid of our battery storage system, we could balance the demand during the day and nighttime by using batteries during the day and recharging it during night.

II. Energy storage system

Power shortage has been becoming a serious problem. Increasing demand on power or electricity, especially during daytime, is undeniably

obvious. On the other hand, nighttime consumption of power is constant of being lower, resulting to an imbalance demand of power that causes power shortage during peak demand.

To somehow bridge his problem, Energy Storage System innovation has been initiated. This energy storage system is a system of how energy or energies are being stored. There are several types of energy storage systems, and these are the following:

Pumped Hydropower

Pumped hydropower facilities consist of two reservoirs at different levels. It then uses electricity to pump water from lower elevation reservoir to higher elevation, thus storing gravitational potential energy. When the electrical energy is needed, the water is released which passes to hydraulic turbines which generates electric power.

Compressed air energy storage (CAES)

This system stores energy by compressing ambient air and stores it under pressure in an underground cavern. To convert this back to electrical energy, the pressurized air is heated and expanded in an expansion turbine which drives an electric generator.

Flywheels

A flywheel storage device stores rotational kinetic energy in a form of spinning mass. The device is integrated by an electrical apparatus which operate as motor to store energy or as generator to produce electrical energy.

Superconducting Magnetic Energy Storage (SMES)

This storage system stores energy in the form of magnetic field. The device is consist of superconducting coil where direct current flows thus, generating and storing magnetic field around the coil. The superconducting state of the coil is achieved by cooling it down below its superconducting critical temperature with the help of cryogenic refrigerator.

Supercapacitors

Supercapacitors are electrochemical capacitors with high energy density and are used in application requiring many rapid charge/discharge cycles. An electrochemical capacitor has components related to both batteries and capacitor. It uses electrolyte instead of solid dielectric and stores energy statically as opposed to batteries which store energy chemically.

Hydrogen Storage

Hydrogen is produced from fossils or by electrolysis of water into hydrogen and oxygen, then compressed or liquefied. If hydrogen is stored in liquid form, a cryogenic storage is required to maintain its liquid form. It is then converted back to electrical energy through a generator.

III. Battery Energy Storage System

Battery energy storage system is another type of energy storage system which uses battery technology for storing energy. This stored energy is being utilized especially during the peak demand of power supply. Thus, preventing power interruption at times when it is needed the most.

Electric batteries are devices that store electric energy in electrochemical form and deliver direct current (dc). For a chemical battery, charging causes a chemical reaction within a battery cell which stores energy in a chemical form. Upon a need of

electric energy, a reverse chemical reaction occurs causing a flow of electricity out of the battery.

The basic components of a typical system will include:

Batteries Converter (DC/AC) Converter Transformer Control System Cooling System

Choosing types of battery is essential for various applications. The most common battery types for renewable energy applications are: conventional lead acid, nickel-cadmium, and lithium-ion. For power grid application, the direct current (DC) stored in a battery should be converted into alternating current (AC) to be able to distribute and transmit electric power. By doing the reverse conversion, the battery will be charged or store energy. The said process will only be possible through the use of a converter which converts DC to AC and vice versa. A converter transformer is also an important component in BESS because it transforms voltage to higher level for transmission and converts voltage to low level for consumption. A control system generally provides complete supervisory control and data acquisition for monitoring the facility. Moreover, it is important to have a cooling system that will maintain the operating temperature of the battery so that it will operates properly and efficiently and removes the intense heat generated by the DC/AC conversion.

IV. Other Promising Battery Technologies

Metal-Air Batteries

Many metal-air batteries have been under a lot of research due to their potential. They are known to be the least expensive type of battery and have high energy and power densities. The most common type of metal-air batteries are zinc-air which has about 1084Wh/kg energy density, and lithium-air with about 2600Wh/kg energy density. However, the major drawback of metal-air batteries is that it has a very low life cycle (~500 life cycles). And despite of the researchers’ efforts in the past two decades, the electrical charging and discharging of these batteries are still very difficult and inefficient.

Redox Flow Batteries

Redox flow battery is an electromechanical system where it uses two solutions with different redox (reduction-oxidation) couples in order to store energy. Vanadium redox flow battery is the most commercialized type of redox flow battery. It has a high efficiency which is up to 85%, and it has a long life cycle unlike the metal-air batteries. However, redox flow battery has a very low energy density which ranges from 20-30Wh/kg.

Sodium-Based Batteries

The two kinds of sodium-based batteries are sodium-sulfur and ZEBRA (NaNiCL) battery. These batteries has high energy density (110Wh/kg), high efficiency (>90), long life cycle and low cost. But, sodium is highly corrosive and that it must be kept protected from moisture thus it has high maintenance requirements.

Lithium-Based Batteries

Lithium-ion is the most used battery nowadays in our electronic devices such as laptops or mobile phones. It is practical to use since it has high power density and efficiency, low discharge rate and quick charging (1-2 hours). Moreover, it has a small size and lightweight, longer life cycle than other batteries and low maintenance requirements.

V. Graphene

One of the materials that might be the new basis of technology revolution is graphene. Graphene was discovered by two researchers Ander Giem and Konstantin Novoselov. It is a monolayer graphite consisting of hybridized carbon atoms. It is a two-dimensional material arranged in a honeycomb crystal lattice.

Moreover, graphene has caught the attention of many researchers around the world. Here's why: It is known to be the thinnest material which is only one atom thick. It would take three-million sheets of it to equal the whip of a pencil tip. Despite being the lightest known material, it is also the strongest. Graphene is harder than diamond and 200 times stronger than steel. It is mechanically flexible, almost entirely transparent, conducts heat and electricity better than any other material and its

semipermeable walls allows nothing to pass through it but water. Furthermore, graphene has many additional properties such as bipolar field-effect, ferromagnetism, quantum hall effect, superconductivity, good chemical stability, outstanding thermal conductivity (3000 W/ (m · K)), high electron mobility (15000 cm2/(V · s)) and excellent mechanical properties.

Recent scientific advancements have allowed development for various methods of preparing graphene. Particularly, in large-scale productions and applications, graphene-based composite materials are analyzed and improved for future development.

VI. Graphene-Based Lithium-Ion Battery

The most important properties of graphene are first, it is very thin that it is considered as a two-dimensional compound. And second, it has the best electrical conductivity thus; it can conduct so much electricity in such a small area. Due to these unique properties, graphene-based nanomaterials are very promising in energy storage applications.

It has been proven that the use of nanomaterials significantly improves the battery's performance in terms of capacity and charge rate, mechanical flexibility, life cycle, and well-developed nanostructures. Graphene therefore can boost high performance of lithium-based storage materials.

How Lithium-ion Batteries Work

Batteries store and release energy by moving electrons from one electrode of the battery to the other, then, the energy from the moving electron does the work. These electrodes are located at the end of the battery. One end is called the anode which is generally made from carbon and the other is cathode from a chemical compound known as a metal oxide (e.g. cobalt oxide).The last battery component is known as the electrolyte, and is located between the two electrodes. In lithium-ion batteries, the electrolyte is a salt solution that contains lithium ions.

When the battery is placed in a device, the positively charged electrolytes are attracted to the cathode, thus moving forward to it. The moment this happens, the cathode becomes more positively charged than the anode, thus, attracting negatively charged electrons.

On the other hand, when the battery is charging, the electrolytes move in the opposite direction. As they move from the cathode to the anode, the battery is restored for another use.

Graphene-Based Materials for Li-ion Batteries (LIBs)

Graphene-based lithium-ion battery has been a subject of research for some time now. The main problem with this study is that graphene anodes cannot provide stable outputs. To circumvent

such problem, variable strategies have been developed. The performances and energy densities of lithium ion batteries largely depend on the chemical and physical properties of the electrodes. Thus, with the special properties of graphene, many researchers attempt to design nanostructures and to in order to achieve higher energy capacity and to increase the battery's discharge and charge rates.

Lithium ions are used as electrolytes in li-ion batteries. But despite being one of the most practical batteries, its materials have some disadvantages that limit their use. Like in carbon materials which is usually used in the anode, have low initial charge and discharge efficiency. Hence, developing a new electrode for anode material is one of the best solution for this problem.

Graphene's chemical stability and high electrical conductivity makes a suitable alternative for electrode material in the battery applications.

Lithium Metal Oxide-Graphene Composites as Cathode Materials for LIBs

Lithium metal oxide-graphene or LiMn2O4

is used as cathode electrolyte material, because of its low cost, high abundance and environmental friendliness. But like any other material, it has a drawback, which is low electrical conductivity which then results to a low-rate capacity. Thus, using graphene as composite material would surely complement its disadvantages. Some studies were made to implement this material including microwave assisted hydrothermal method and self-assembly approach combined with a solid-state lithiation method. Results show enhancements in electrochemical properties due to faster diffusion and greatly improved stability.

Lithium metal oxide-graphene composites or LiNi1/3Mn1/3Co1/3O2 is a promising candidate for cathode electrode materials. It has shown higher energy density, better stability, enhanced safety as well as low cost. However, during calcinations, cation disorder occurs resulting in deterioration of its kinetic properties. To improve its electrochemical performance, graphene composites are prepared by mechanical mixing and could deliver a capacity of 115 mAh/g. The improved performance of the battery is attributed to the high electrical conductivity and grain connectivity.

LiMPO4-Graphene Composites as Cathode Materials for LIBs

Lithium iron phosphate, LiFePO4 has of high specific capacity (170mAh/g), low toxicity and low cost. However, capacity fade quickly under high rate charge and discharge due to its poor lithium ion diffusion (10- 14-10- 16 cm2/S) and low electrical conductivity (10- 9S/cm2). The addition of graphene to improve the electric properties of the phosphate was based on its conductivity and mechanical properties which maintains the microstructure of the phosphate and improves stability. Moreover, graphene's flexibility improved its ratio performance. The LiFePO4-graphene nanocomposite was prepared by various synthesis routes, with hydrothermal, solvothermal and solid state routes. In addition, the researcher also generated LiFePO4

(LFP) nanoparticles, mixed them with graphite oxide in solution which then underwent a spray-dried and sintered process to obtain the LiFePO4/graphene composite (LFP/G). The obtained material displays a more regular morphology and structure, which can lead to enhancing the electric conductivity of the batteries. In addition, carbon coating this material obtains LiFePO4/graphene (LFP/(G + C)), which presents superior rate and cycle performances.

Graphene Nanoflake Ink

In this method, a thin film of graphene, prepared by Chemical Vapor Deposition (CVD), was dispersed in N-methyl-2-pyrrolidone, an appropriate organic solvent. Then, the dispersion was treated with ultrasound (ultrasonication) which formed graphene flakes of various dimensions. After this, the researchers ultracentrifuged the dispersion at 25000 rpm in order to separate the larger flakes from the smaller ones. The smaller and lighter flakes remained suspended in the solution while the larger graphene flakes sedimented at the bottom. At the end of the ultracentrifugation, the liquid remaining above the residue at the bottom was separated by pipetting. This liquid, called supernatant, contained graphene flakes with the dimensions ranging between 30-100 nm. Drops of the suspension was carefully placed, which was now spreadable graphene ink, on the surface of a copper substrate. The metal was heated at 400 oC, to completely remove the solvent, which only leaves graphene. Lithium-ion battery anode, and LiFePO4 as cathode were used.

During testing, this lithium-ion battery showcased excellent boosts in performance, as its energy density was 190 W h kg-1 which is about 25 % higher than that of lithium-ion batteries used.

Lithium-Ion Battery Based on a Graphene Anode and a Lithium Iron Phosphate Cathode

Graphene-based nanocomposites have been determined as promising high-performance anodes for lithium ion batteries to meet the ever-growing demands for higher power and energy.

An advanced lithium-ion battery based on a graphene ink anode and a lithium iron phosphate cathode was established by balancing the composition of cells and suppressing the initial irreversible capacity of the anode in the round of few cycles. An optimal battery performance was demonstrated in terms of energy density which is about 190 Wh kg–1, specific capacity of 165 mAhg–1, and a stable operation for over 80 charge–discharge cycles. Aside from low cost components, the battery is also potentially scalable. As we know, graphene-based lithium ion batteries having high-rate performances are rarely reported; hence, the results showed in this research may open up new

NANO-GCA

The NANO-GCA (Gradual Channel Approximation) has a specific capacity of around 2000 mAh/g, when graphite anodes have a theoretical capacity of only about 372 mAh/g. This can be achieved by mixing with other conductive additives. These materials are backed by the first IP on graphene-enhanced anodes for Li-Ion batteries which mean that graphene enhanced anode materials can be produced without limitation taking advantage of graphene’s mechanical, electrical, and thermal properties.

VIII. Improvements in Battery Energy Storage System Application

Power Quality and Capacity

Consumers, especially information services, financial, and telecommunications businesses, demand high quality, reliable power to run electronic devices.

Power quality of an electric power supply is determined by available reserve capacity at the energy utility. The energy system should have a reserve energy so that when the load level exceeds the power generation, the voltage will not decline

which may disturb the normal operation or even cause damage to the customer’s equipment.

Due to high flexibility and very short response time provided by the BESS, the power plant can be able to provide instantaneous power reserve and can be used to balance the load as well. These benefits of the energy system results an improved power quality of the energy delivered and could guarantee high reliability to the customers.

Renewable Energy Integration

One of the many areas of applications that graphene could further improve is the renewable energy integration. Wind and solar energy are the main sources of renewable energy and are known to be intermittent. This is because they are sensitive to time and weather, and geographic locations and features. Being intermittent, these energy sources often cause fluctuations that make them an unpredictable source of energy. Moreover, the generation and load's imbalance results to additional financial costs.

But, with graphene's lithium-ion batteries, energy storage systems could be purposely designed to facilitate an effective integration of both small and large-scaled renewables. With this, we could achieve easier integration and much higher stability for our renewable energy sources.

Time-shift of Energy Delivery

One of the most common problems for both conventional and renewable generation is balancing generation and the load. By realizing this, cost savings would be much higher. Time-shifting energy allows servers to change the source of energy which usually is the energy storage system with low cost generation and discharge during high generation and high demand periods. Using graphene based battery storage, costs could be greatly reduced in terms of capital life expectances and operational inefficiencies. Additionally, the storage system would have faster response time.

Grid Support and Compatibility

In a traditional power grid operation, storage systems help maintain reliability and power quality. This then, reduces efficiency losses and produce smooth and coordinated operation of grid components. With the help of graphene, all these

services could be further improved and that we could have higher energy systems that would be able to provide capacity firming, thus, making energy production predictable. By this, we could solve or reduce power fluctuations and power stabilizations.

Cost Savings for Home and Business

Using batteries for home or business enhances cost savings and creates optimized management of local energy consumption and production in homes and small buildings.

Furthermore, graphene's mechanical flexibility could help in energy storage solutions. Take for example, once the battery in our cell phones or laptops is broken, it is highly unlikely to be fixed. Even nowadays, if the battery is broken, we always buy a replacement. Now, with the special properties of graphene, modular batteries for our electronic devices are possible. With its modularity, the batteries can easily be assembled and repaired.

IX. Conclusion

Since electronic devices nowadays have significantly changed, the industries strived to develop smaller and lighter yet faster products. Large electronic companies compete in implementing more efficient hardware such as high-performance batteries. Lithium-based batteries are widely considered due to its ability to charge as many times as the user needs. The safety, cost, performance and chemical properties of the lithium ion batteries are mainly considered when engineers design a hardware. To increase the efficiency of the batteries a combination of nanoparticles and graphene is recently introduced. Results and simulations of it have shown to have enormous technological effect and are aggressively improving the durability and performance of the batteries. However, due to very high electronic conductivity, these materials can be thought of as preparing the anode electrode in the lithium ion battery.

With graphene-based batteries used as an energy storage, significant improvements can be made with regards to power and energy problems. It could end up being fairly economical as time goes on and production becomes more widespread. 

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A. Joseph and M. Shahidehpour, “Battery Storage Systems in Electrical Power Systems”, 2006. (references)

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http://www.researchgate.net/publication/265139107_Graphene-based_nanocomposite_anodes_for_lithium-ion_batteries

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