Li-ion batteries take leading role in energy storage apps

Li-ion batteries take leading role in energy storage apps

Water-based processing and new large format form factors will help expand Li-ion adoption in many key industries

BY JACOB MUTHU
International Battery, Allentown, PA
www.internationalbattery.com

Performance, cost, availability, and safety of energy storage systems can often change power system designs. As electric vehicles and the smart grids transform their respective industries, the role and significance of storage batteries continue to increase.

Beta testing confirms the value proposition and desirability of large-format prismatic lithium-ion (Li-ion) battery chemistry, footprint, rechargability, and thermal properties when paired with battery management system (BMS) technology. These batteries are well suited for applications such as military vehicles on silent watch, backup power for NASA ground operations, renewable energy, micro grids, telecommunications, forklifts, tractors, medical devices, and marine systems with the goal of using smaller generators and less fossil fuel.

In renewablenergy applications, for example, energy storage can be a major part of a renewable system’s cost. Evaluating all technologies and chemistries, from fuel cells to large-format batteries remains a focal point for today’s system architects and designers needing to create a favorable value proposition to move ahead with their green projects. One example is International Battery, a domestic manufacturer of large-format Li-ion batteries and systems has been responding to numerous requests to quote on small 24-V systems as well as larger 48-V (and up) systems. Smaller systems, originally designed for diurnal storage of solar and wind power generation, have also shown popularity for remote location energy needs during grid failure, reducing the load on backup generators.

Real world tests

In Maui, Hawaii, an interesting project using energy storage has been recently deployed to assess the effectiveness of storing solar energy using Li-ion battery technology. The renewable-energy system is composed of sixty 224-W photovoltaic panels, a bidirectional three-phase inverter system and a state-of-the-art charge-controller network provided by HNU Energy in Maui. A 48-V, 16.4-kWh Li-ion–based energy storage system was integrated — complete with battery management and controls – to store the energy generated from the solar array (see Fig. 1 ).

Fig. 1. Energy generated from a solar array is captured in a Li-ion-based energy storage system.

The energy storage system includes four battery modules, totaling 32 160-Ah lithium iron phosphate (LFP) cells and a BMS that is integrated into a standard 19-in. portable rack-mount chassis and enclosure. Large-format Li-ion batteries were chosen for this project because of their proven high-energy density, robust thermal and cycling performance as well as easy system expandability.

For demanding military applications, Li-ion batteries offer superior cycle life and operating temperature fluctuations experienced in rugged operations with less availability to charging stations. Maintaining life in constrained space is also superior to other battery chemistries. Moreover, the long-range value proposition is better due to less field replacement reducing support logistic expense in keeping with the Department of Defense’s “more fight-less fuel” strategy. For example, to avoid infrared detection, Silent Watch goals are to have the ability to shut engines down and still have power beyond 10 hours with a small battery footprint and be thermally managed without forced cooling.

Greener manufacturing

Traditionally, Li-ion electrodes are made using a slurry-based process, which uses large amounts of organic solvents to homogeneously mix the components of active materials (see Fig. 2 ). The solvent predominantly used in the Li-ion industry is N–Methylpyrrolidone (NMP). However, the use of some organic solvents is undesirable because of the high cost associated with environmentally compliant handling and disposal requirements, the added material and capital cost for the manufacturing process and the toxicity of the solvent.

Fig. 2. Li-ion electrodes are made using organic solvents that are expensive to dispose of in an environmentally compliant manner. New water-based processing reduces the cost.

A significant advancement has recently been made with water-based processing aimed at reducing battery costs and protecting the environment at the same time; giving designers a greener choice when specifying Li-ion batteries.

At International Battery, the focus is on manufacturing Li-ion cells using a water-soluble binder (WSB)–based process for both the cathode and anode. By eliminating the solvent from the manufacturing process, the material cost and capital investment cost can be reduced considerably. The WSB process uses water as a medium to dissolve and disperse the binders and the electrode materials, respectively, as opposed to solvent-based process which require additional recovery equipment, hoods and other VOC precautions as necessary.

Battery chemistry considerations

While there are several choices for energy storage for a variety of applications, design engineers and system designers need to consider weight, footprint, modularity, cycle life, service/maintenance, charge times, and capacity loss. Moreover, the following should be carefully considered:

Safety . Lithium iron phosphate (LFP) is used and is recognized as the safest lithiated cathode material. One of the few companies that has been using LFP for several years, International Battery cooperates with licensed suppliers on the continuous improvement of the material. Cell design comprises proprietary pressure release system that along with other design innovations provide a reliable and safe cell. The electrode system should be able to sustain cell potentials even during overcharge without ignition and thermal runaway.High-abuse testing . Look for extensive testing under abuse conditions exceeding U.S. ABC requirements to ensure product meets the abuse safety requirement of the application. Large-format prismatic iron phosphate cells can be abused to somewhat extreme conditions without the risk of explosion or the high temperatures other chemistries experience. Look for testing by third-party labs. A battery management system (BMS) that actively monitors and balances the cells providing high system efficiency and should interlock with the system’s isolation system for redundant safety functions.Thermal management . Consider built-in heat sinks or an electrical buss that does not contribute heat generation to the system and allows low resistance maintenance-free cell interconnection.Special testing . Don’t overlook shipping certifications. For example, UN Transportation Testing U.S. Department of Transportation (DOT) and its international counterparts responsible for regulations that govern the transportation of hazardous materials base their regulations on the UN Recommendations on the Transport of Dangerous Goods Model regulation and UN Manual of Tests and Criteria.Environmental impact . Li-ion batteries are experiencing wider adoption and can be recycled allowing lithium to be reclaimed, reducing the need to further mine lithium salts. Eco-friendly rechargeable large-format lithium batteries, if properly maintained and charged/discharged, have a life expectancy of 10 years as opposed to lead acid counterparts, which are discarded after one mission such is the case in military usage. Also, look at the location and process by which batteries are manufactured. Are we actually putting more toxins and pollutants in our environment in the quest to be green?

Larger is better

Another important advancement is the development of large-format prismatic battery cells. Different from their smaller cousins used in flashlights and iPods, large-format Li-ion prismatic batteries (see Fig. 3 ) provide more optimal building blocks to deliver higher amounts of energy and scale up as energy demands increase.

Fig. 3. Large-format Li-ion prismatic batteries.

Designing a battery system with large-format prismatic cells mean fewer connections and less wiring, which reduces cost, improves thermal management and maintains a high energy density of the system. With large-format prismatic cells, each individual cell can be monitored enabling the BMS to more precisely know the state of the battery and provide active balancing of the cells. This advanced monitoring and management results in a more efficient use of the stored energy in the system. Using state-of-the-art software and electronics, today’s advanced battery-monitoring systems can tell users the exact state of the battery, state of health, charging status and temperature.

The future

As exciting applications such as electric/hybrid vehicles and smart-grid energy storage requirements drive innovations and transform their respective industries, the role and significance of Li-ion batteries continues to increase.

From an economic and environmentally sustainable perspective, the future looks very bright for energy storage incorporating Li-ion cells. Based on performance results and cost analyses, water-based processing and new large-format form factors will help expand Li-ion adoption in many key industries. ■