Battery Options for EVs
Despite the fact, the EVs had early comers advantage over ICEVs & ruled the mobility world before the rise of ICEVs, yet the rechargeable batteries back then were not efficient, difficult to handle, and were not economical. The rise of Henry Ford’s mass-produced affordable & reliable ICEVs pulled the plugs for the EVs, which by the 1950s slowly died their natural death. With EVs gone, went the associated battery development for EVs. Fortunately, the quest for stored portable energy never died and with the rise of the semiconductor & electronics industry in 1970, the need for long-serving, low cost safe & high performance batteries was more seriously felt. While the battery technology grew rapidly, serious environmental impacts of burning the fossil fuel in ICEVs also started becoming prominent (global warming, ozone layer depletion, fall of AQIs in cities, etc.). With the development of many new battery technologies in the last few decades as well as the miniaturization of electronics, the beginning of the 21st century was ripe for EVs to bounce back for their righteous place.
Unlike early 1900, this time the situation was much different as while the battery segment by itself had grown rapidly offering multiple technologies, almost all giants in the ICEV makers were also investing heavily in developing their energy technologies.
While each of these technologies has its own set of advantages & challenges. Let us try to briefly understand some of them as The “War of the Batteries”, has just begun.
Classification or Application of Various Batteries Used in EVs: The current batteries which are used in current EVs can be broadly classified as below:
Secondary Batteries – Rechargeable
Lead Acid Battery (LAB)
These are the cheapest energy sources and, in the past, most commonly used batteries in EVs like forklifts, golf carts or e-rickshaws. Being heavy LABs, they increase the vehicle weight by 25% to 50%. They also have much lower specific energy than petroleum fuels (30–50 Wh/kg) as well as their storage capacities decreases with lower temperatures. These batteries have powered early modern EVs e.g. General Motors’ EV1 electric car produced between from 1996 to 1999. However, with much better options available the LABs are not used in modern EVs.
Advantages
- Flexible Shapes And Sizes
- No Maintenance (for Sealed LAB only)
- High Reliability And Working Capabilities
- Long Shelf life With Or Without Solvent
- Longest Life Cycle
- About 97% Recyclability
- Low Cost &
- Lowest Self Discharge Rate
- Easy To Manufacture
Disadvantages
- Heavy Weight Battery Due To Lead
- Not Environmentally Friendly Due To Lead
- Low Specific Energy, Poor Weight To Energy Ratio
- Has Slow Charging Rate
- Typically Emit Corrosive & Explosive Hydrogen, Oxygen And Sulfur Gases
- Must Be Stored In Charged Condition To Prevent Sulfation
- Transportation Restrictions On Flooded Type LAB
Nickel Metal Hydride Battery (NiMH)
These batteries now have mature technology. Though they are less efficient (60–70%) in charging and discharging than even LAB they have far higher specific energy ratio of 30~80 Wh/kg and despite proving their longevity in Toyota’s first-generation RAV4 EVs that still operate well after 100,000 miles (160,000 km) and over a decade of service as well GM using them in its second generation EV-1, NiMH did not become a popular choice of EV makers due to poor efficiency, high self-discharge, very tricky charge cycles, and poor performance in cold weather. As per news Toyota is also now planning to shelve this technology.
Advantages
- Has Higher Energy Densities
- Profitable For Recycling
- Simple Storage And Transportation
- Environmental Friendly-Contains Only Mild Toxins
Disadvantages
- Limited Service Life
- Limited Discharge Current &High Self-Discharge
- Generates Heat During Charge
- Requires Regular Full Discharge To Prevent Crystalline Formation.
- Prone To Memory Loss
- Performance Degrades At Higher Temperatures
- Trickle Charge Is Critical & Needed Careful Control
Sodium (Na) Nickel Chloride Battery (ZEBRA Battery)
IN 1985, this battery was developed by Zeolite Battery Research Africa, hence the name ZEBRA which was later expanded differently as Zero Emission Battery Research Activities. It contained electrolyte of molten Sodium tetrachloro-aluminate (NaAlCl4) salt and has with a specific energy between 90-120 Wh/kg. Pre heating of Sodium salt is must. These cells are proved to be highly reliable with cell failures virtually to be non-existent. Though they have been used in few EVs produced by now closed MODEC Inc. (Mitsui Ocean Development & Engineering Company Inc.) from UK yet due to many inherent factors they could not become a favoured choice of EV makers & the development refocused almost exclusively on the higher voltage variants.
Advantages
- High Energy Density >110Wh/Kg
- Capacity & Performance Are Independent Of Discharge Rate & Temperature
- No Self Discharge
- Cells Do Not Short Circuit
- High Energy Density (>5 Times Than LAB)
- Single Cell Failure Does Not Cause Complete Battery Failure
- Maintenance Free, Fully Sealed, No Gassing
- Long Storage & Operational Life
- >2000 Cycle Life At 100% Capacity
Disadvantages
- High Cost
- Preheating To 270DegC Needed To Get Battery Functional
- Large Capacity Batteries Only (>20KWh)
- High Internal Resistance
- High Operating Temperature
- Uses 14% Of Its Own Capacity To Maintain Temperature Even When Not In Use
- Needs Thermal Management System
- Only One Manufacturer In The World
Lithium-Ion Battery (LIB)
Lithium is the lightest of all metals and has the greatest electrochemical potential to provide the largest energy density for weight but Lithium metal also has inherent instability during charging when used in the battery. In early 1970, M. Stanley Whittingham discovered the process to control this charging instability. However, he could not make this rechargeable lithium battery a practical one. During 1974~76, a process of reversible intercalation in graphite and intercalation into cathodic oxides was discovered by J. O. Besenhard who proposed its application in lithium cells. The research work continued on these cells and in 1991 when a Japanese team at Sony, led by Yoshio Nishi who successfully released the first commercialized lithium-ion battery. The development of LIB technology was considered to be so revolutionary that in 2019, the Nobel Prize in Chemistry was awarded to John Goodenough, Stanley Whittingham, and Akira Yoshino “for the same. Though these batteries are called LIBs, in real terms they do not have any Lithium as metal but as intercalated lithium compound. These LIBs are extensively used in modern EVs, however battery technology analyst Mark Ellis of Munro & Associates sees three distinct LIB form factors & their combination that would be used in future EVs: a) cylindrical cells (e.g., Tesla), b) prismatic pouch (e.g., from LG), and c) prismatic can cells (e.g., from LG, Samsung, Panasonic, and others).
Advantages
- High Energy Density
- Does Not Need Prolonged Priming When New
- Relatively Low Self-Discharge
- Low Maintenance
- Can Provide Very High Current To Needed During Quick Acceleration
- No Memory
- Higher Cell Voltage (3.6V)
Disadvantages
- Subject To Aging, Even If Not In Use
- Requires Protection To Maintain Voltage And Current
- Expensive To Manufacture
- Transportation Restrictions
- Not Fully Mature – Metals And Chemicals Are Continually Changing
- Need Storage In A Cool Place
Lithium Polymer Battery (LPB)
The lithium-polymer battery the electrolyte is made of a polymer resembling a plastic-like film that does not conduct electricity but allows ions to flow freely. The polymer resembling film offers simple fabrication with ruggedness & safety as well as a thin-profile geometry. With a cell thickness measuring as little as one millimeter (0.04 inches), equipment designers are left with their imagination in terms of form, shape, and size. Unfortunately, the dry lithium-polymer suffers from poor conductivity & the internal resistance is too high which cannot deliver the current bursts needed to power modern EVs. Lithium-ion-polymer has not caught on as quickly as some analysts had expected. Its superiority to other systems and low manufacturing costs has not been realized. No improvements in capacity gains are achieved the capacity is slightly less than that of the standard lithium-ion battery. Lithium-ion-polymer finds its application only in a niche market requiring waferthin geometries, such as batteries for credit cards and other such applications. Some car manufacturers e.g. Hyundai Motor Company & Kia Motors also used this type of battery in their BEVs & HEVs.
Advantages
- Very Thin Profile Possible
- Flexible Form Factor
- Lightweight
- Excellent Storage Stability
- High Energy Densities
- Hermetically Sealed-No Gassing Or Leakage
- Wide Operating Temperature Range
- Shock And Vibration-Resistant
Disadvantages
- Lower Energy Density
- Expensive To Manufacture
- Higher Cost-To-Energy Ratio
- The Capacity Decreases Gradually On Cycling
- Low Current Drains
- Power Output Reduced At Low Temperatures
- Care Must Be Exercised To Prevent Short
Solid State Battery (SSB)
A SSB is a rechargeable battery that uses solid electrodes (made of materials like ceramics e.g. oxides, sulfides, phosphates) and solid electrolytes (made of solid polymers) instead of using liquid or polymer gel electrolytes that are found in LIB or LPB. Despite that the solid electrolytes were first discovered by Michael Faraday between 1831 and 1834, it had several shortcomings e.g. low energy densities, low cell voltages, and high internal resistance, which allowed their use for limited application like pacemakers, RFID, and wearable devices. Improvement of the technology in the late 20th and early 21st century brought back interest in SSB battery technologies, especially when EVs are becoming the new normal.
With more than 1,000 patents, Toyota stands at the top of the global chart when it comes to SSB technology development and is already working to introduce an EV driven by these SSB by this year end to cover 500 km range on a single charge with fast charging capability of zero to full in 10 minutes, all with minimal safety concerns. Ford and BMW have also announced to invest $130 million in SSB driven EVs. While Nissan too has plans to develop its own SSB by 2028.
Advantages
- Much Safer
- Much Faster Charging Speed
- High Charging Cycles
- Much Higher Energy Density
- No Dangerous Or Toxic Substance
Disadvantages
- High Cost
- Need To Be Proven In Real World Conditions
- Mass Production Processes Are Not Yet Established
- Durability Need To Be Established
- Requirement Of Higher Rating Charging Infrastructure
- Temperature And Pressure Sensitivity
- Decay Due To Growth Of Dendrites
…To be continued
Prabhat Khare possesses a BE (Electrical) degree from IIT Roorkee (Gold Medalist). Now, he is the Director of KK Consultants. He is also a BEE Certified Energy Manager and a Lead Assessor for ISO 9K, 14K, 45K & 50K.
