Battery-Supercapacitor Hybrid Energy Storage Systems

INTRODUCTION

Batteries are used as energy storage devices in multiple applications. However, batteries have certain disadvantages, such as low power density, limited life cycle and comparatively slow response in the context of certain applications. The feasibility of using a battery may be limited when dealing with transient high-power demands, such as the output power and load variability from transient renewable energy sources (RES). This may lead to an oversized design of batteries, resulting in increased investment cost and additional power loss due to the slow response of the batteries while compensating for transient peak power demands.^[1]

Electric vehicle (EV) batteries are particularly prone to degradation due to high peak power and harsh charging/discharging cycles during acceleration and deceleration. Moreover, battery-powered electric vehicle (BEV) applications require high power, resulting in an oversized battery pack and less optimal use of energy.^[2]

Supercapacitors (SC), on the other hand, do not store as much energy as batteries; and have the ability to accumulate and release the energy very rapidly. These devices are suitable for high power vehicle applications, for providing power that is required to accelerate the vehicle or recover the available energy during braking phase. Supercapacitors cannot be used as the sole power source for EVs, as they have low energy density compared to batteries. However, they provide good options to compensate for the high peak of usage during short periods of time when battery power is not sufficient.^[3]

Battery-Supercapacitor Hybrid Energy Storage System (HESS)

Battery-supercapacitor hybridization helps overcome the limitations of batteries or supercapacitors. It reduces the stresses applied to batteries, thus improving their life.^[4]

The hybridization of the embedded energy storage systems provides the following advantages:^[4],[5]

• Improved Li-ion battery lifetime
• Maximized energy recovery during braking
• Reduced size of embedded energy storage system
• Reduced cost of embedded source

Battery-Supercapacitor Hybrid Energy Storage Systems in Electric Vehicles

Electrification is an important means of decreasing greenhouse gas emissions in the transportation sector. The global electric car fleet has now exceeded 5 million and will continue to increase in future. The energy storage system is a critical part of the electric vehicle. The storage system has to be cost-effective, light, efficient, safe, reliable, occupy less space and have a long life. It should also be produced and disposed of in an eco-friendly way.^[6][7] Interestingly, electric vehicles can be used as back-up storage during periods of grid failure or spikes in demand. Elverlingsen in Germany collects almost 2,000 batteries from Mercedes Benz EVs to create a stationary grid-sized battery that can hold 9 MW of energy.^[8]

The lithium-ion (Li-ion) battery technology plays a major role in EVs due to its power and energy density. Supercapacitors (SC) possess extremely high-power density, high cycle time, cycling efficiency and low energy density. Connecting battery pack with supercapacitors is considered to be an effective method to provide energy and power for EVs and Hybrid Electric Vehicles (HEVs) as it results in both high power and high energy capability.^[9][10][11]

RECENT DEVELOPMENTS

CRE Technologies has developed a hybrid supercapacitor battery that is useful for memory backup, energy storage for short-term operation, power for long-term operation and instantaneous power, for applications that require relatively high current units up to several hundreds of amperes.^[12]

American Lithium Energy Corporation (ALE) has developed a lithium-ion supercapacitor hybrid cell that combines the capacity and energy of lithium-ion cell with the power and cycle life of a supercapacitor. Since it has components of both, a lithium ion and a supercapacitor, it is able to rapidly cycle without decay. These hybrid cells not only enable rapid discharge, but also fast charging.^[13]

NASA’s Marshall Space Flight Center has developed a novel solid-state supercapacitor with a unique combination of high capacitance and battery-like discharge characteristics. This is to replace range-safety batteries used to power the systems that destroy off-course space launch vehicles. Other commercial applications include rechargeable batteries for use in electric vehicles.^[14]

ESTACA, a French Engineering School, has been actively working on a Hybrid Energy Storage System (HESS) Multiphysics model (Fig.2), developing and designing new energy management strategies based on battery/supercapacitors for electric vehicles with improved thermal battery behavior.^[15]

Fig.2 Multiphysics model of the hybrid energy storage system

Zheng, JS., et al. developed a new hybrid electrochemical device based on a synergetic inner combination of Li ion battery and Li ion capacitor (HyLIC) as shown in Fig.3, with high energy density, long cycle life and excellent power density for electric vehicles.^[16]

Fig.3 Schematic of Hybrid Li ion capacitor (HyLIC)

Vlad, A., et al. designed high energy and high-power battery electrodes by hybridizing a nitroxide-polymer redox supercapacitor (PTMA) with a Li-ion battery material (LiFePO₄) with enhanced power density and energy density, and superior cycling stability for electric vehicles.^[17]

Anne-Lise Brisse, et al. worked on nanocomposites of Ni(OH)₂ or NiO-based positive electrodes in hybrid supercapacitors operating under KOH (electrolyte), together with an activated carbon-negative electrode. They noticed that such nanocomposite electrodes can successfully improve the performance of standard Ni(OH)₂ (+)//6 M KOH//activated carbon (-) hybrid supercapacitors.^[18]

Researchers from North-West University and Queen’s University Belfast proposed the design of hybrid energy storage systems by combining supercapacitors (SCs) and lithium-ion capacitors (LiCs), i.e., hybrid capacitors (HCs), with a battery through a multiple input converter for electric vehicles. Efficient combination is facilitated using a multiple input DC–DC converter.^[19]

Design of the system is shown in Fig.4:

Fig.4 Overview of the concept design (Highlighting the major focus areas of the above research)

COLLABORATIONS

Duke Energy | Aquion Energy | Maxwell Technologies

Duke Energy has collaborated with Aquion Energy, Maxwell Technologies and others to build a hybrid energy storage system (HESS) project. The hybrid system uses Maxwell’s supercapacitors to help manage solar smoothing events in real-time, particularly when the solar power is on and the grid fluctuates due to cloud cover or other weather circumstances. The Aquion batteries are used to shift solar load to a time that better benefits the utility. The hybrid energy storage system integrates patented energy management algorithms.^[20]

Hitachi Ltd. | Shin-Kobe Electric Machinery Co. Ltd.

Hitachi Ltd. has been working on the development of hybrid battery energy storage systems. It has developed a hybrid battery energy storage system by combining lead-acid batteries that can provide high capacity, safety and low cost, and lithium-ion capacitors that feature the ability to respond to sudden fluctuations with high charge-discharge cycles. The company has co-developed a 1.5 MW hybrid battery energy storage system with Shin-Kobe Electric Machinery Co. Ltd. (now Hitachi Chemical Company Ltd.).^[21]

Automotive Research Association of India | Indian Space Research Organization

Automotive Research Association of India (ARAI), in collaboration with Indian Space Research Organization (ISRO), has developed the Tata Hybrid Magic vehicle featuring a unique hybrid energy storage system that combines a conventional battery pack with supercapacitors supplied by ISRO. It was showcased on the Tata Ace platform at the Auto Expo 2020. The Tata Magic hybrid prototype (Fig.5a and 5b) can provide a range of roughly 120-150 km on a full charge with the supercapacitor of a smaller size alone, providing 40% of the total energy required by the vehicle. This results in reduction in weight and cost, and improved battery life.^[22]

Queensland University of Technology | IIT Jammu | TU Munich

Researchers at the Queensland University of Technology, in collaboration with IIT Jammu (India) & TU Munich (Germany), have developed a supercapacitor-based energy storage device with a power density of about 10x that of lithium batteries and an energy density close to that of nickel-metal hydride batteries. This novel supercapacitor device has a capacitor-type titanium carbide-based negative electrode and a battery-type graphene-hybrid positive electrode. According to researchers, this invention may replace the lead-acid board net batteries that are still required in today’s lithium-powered electric vehicles.^[23]

Beyonder | ABB

Beyonder and ABB have collaborated to pave the way for strengthened product development, production and market strategies for mass production of Beyonder’s Lithium-ion capacitors (LiC) using key components from both parties. Beyonder and ABB will work together to explore a more cost-effective and sustainable way to deliver energy storage solutions for the power grid, and support emission-free solutions at airports, ports, heavy transport and fast charging stations.^[24]

START-UPS

C2C-NewCap

A spin-off from the Instituto Superior Técnico – University of Lisbon, C2C-NewCap develops electric energy storage solutions. It is currently manufacturing pilot-scale supercapacitor modules based on a proprietary electrode technology (Fig.6). This Company produces a supercapacitor module specially designed for engine starting – Go-Start – with Nickel-Carbon electrodes and an aqueous-based electrolyte. Go-Start modules are fitted with two cylindrical-shape battery-type connectors for easy installation in any vehicle or industrial equipment.^[25]

Fig.6 C2C-NewCap’s System

Skeleton Technologies GmbH

Estonian startup Skeleton Technologies GmbH is teaming up with the Karlsruhe Institute of Technology (KIT), one of Germany’s major research and educational institutions, to develop a “SuperBattery” that features a 15-second charge and has a huge potential in the application field of electric vehicles. This energy storage system is a hybrid of a lithium-ion battery and supercapacitor made with ‘Curved Graphene’, which is the Skeleton’s patented carbon material.^[26]

Beyonder

Beyonder, founded in 2016, is a Norwegian energy tech company that develops the next generation of sustainable Li-ion capacitors and supercapacitors for the heavy-duty industry sector. By a combination of a Li-ion cell and a capacitor, Beyonder’s batteries perfectly suit many applications where conventional batteries are not powerful enough, or too expensive in their total cost of ownership. The application spectrum ranges from UPS applications (uninterrupted power source) over buffers for wind or solar parks and mobility applications with high start-up currents (ferries, buses, construction machinery, etc.).^[27]

RECENT PATENT PUBLICATIONS

US20190260104A1 – American Lithium Energy Corporation has developed a system, method and apparatus of battery and supercapacitor hybrid that contains a first hybrid electrode comprising a battery electrode, a current collector, and a supercapacitor electrode, a second hybrid electrode and a separator interposed between the first hybrid electrode and the second hybrid electrode. Different combinations and sub-combinations of hybrid systems have been provided. Diagrammatic representations of a few are shown below:

Fig.7 Different arrangements of hybrid electrodes

The first electrode is formed by porous disordered carbon and/or graphitized carbon and the supercapacitor electrode is formed by disordered carbon and/or lithium titanate spinel. Aluminum (Al), copper (Cu), copper (Cu) alloys, nickel (Ni), titanium (Ti), stainless steel, graphene, and carbon (C) nanostructures with or without combination is used as first current collector. Solid state electrolyte, and/or a liquid electrolyte in an ethyl carbonate (EC), dimethyl carbonate (DMC), and/or diethyl carbonate (DEC) solvent is used as electrolyte material.

US2019148714A1 – Cambridge Display Technology Limited and Sumitomo Chemical Company Limited have developed a design and method of producing improved polymer-based electrode layer morphology which results in improved charge-storage and current output of thin film charge storage device. The charge storage device can be a thin-film battery, an electrochemical capacitor or a battery-supercapacitor hybrid.

CN111312526A – Fujian Institute of Research on The Structure of Matter and Chinese Academy of Sciences have developed a preparation method of battery-supercapacitor hybrid energy storage device. This device is made up of a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator between the positive and the negative electrode sheets. The active material in the negative electrode slurry comprises of a carbon material that is modified with an anthraquinone compound and electrolyte is an aqueous solution containing divalent manganese ions and sulfuric acid.

CN112104060A – CRRC Qingdao Sifang Vehicle Research Institute Co. Ltd. has developed an energy control method for a Li battery-supercapacitor hybrid energy storage system of a tramcar to avoid overcharge of the hybrid energy storage system. The controller of the tramcar obtains information pertaining to the condition of the super capacitor and the lithium battery and judges whether the state of the super capacitor and lithium battery is normal or not and then generates closing instructions for controlling the contactor and ensuring that the charge states of the super capacitor and the lithium battery are in a reasonable range.

CN112118049A – CRRC Qingdao Sifang Vehicle Research Institute Co. Ltd. has developed an optical fiber ring network communication method used for a tram hybrid energy storage system to improve data transmission efficiency.

CN112104061A – Global Energy Internet Research Institute Co. Ltd., State Grid Co. Ltd., State Grid Beijing Electric Power Company, and Guoneng Tonghui (Beijing) Technology Co. Ltd. have developed a method of distribution of energy for a lithium battery-supercapacitor hybrid energy storage system which is useful in electric vehicles. Advantages of the present method include reduction of load pressure of the energy storage battery, and fluctuation frequency of the charge and discharge current. Further, service life of the energy storage battery is extended and the system maintenance cost is reduced.

CONCLUSION

Hybridization of supercapacitors with battery systems can overcome the limitations in both the thermodynamics and kinetics of the electrochemical reactions involved in the battery technologies as they do not fully meet the requirements of irregular energy consumption of vehicles. Improved supercapacitors and their variants present huge opportunities in minigrids, trains, trams, trucks, heavy off-road vehicles, tiny uninterruptable power supplies for IoT nodes and  1 MWh giants for hospitals and data centers. They already drive brain scanners, lifts, Maglev trains, power rail, laser guns, vehicle brakes, aircraft and bus doors. Currently researchers are working on the opportunities for designing native battery/supercapacitor systems and development of eco-friendly hybrid and electric vehicles. Challenges still exist in the form of requirement of novel electrode materials, such as silicon-based, nanocarbon-based, etc., implementation of novel coating methodologies such as 3D printing and inkjet printing to reduce the thickness, and so on; so as to promote utilization of supercapacitors on a commercial scale.

AUTHORS

Dr. John Kathi

Ms. Nirmala Kadali