Electric vehicle batteries (6)
Whilst electric vehicles were commonly used from 1880 or so, and until the early 1920s that which precluded any major to them (see Electric Vehicle History) was no truly major increase in the energy storable in rechargeable batteries. This also limited speed (in passenger cars) to only 35 km/h or so, and a range of little over 100 km. It also awaited adequate control technology.
Pic: Edison Battery Archives
From 1970 onward, that control technology improved dramatically, as did that of cell batteries. The energy available from rechargeable batteries increased slightly with the introduction of AGM batteries in the late 1970s but by and large the size, weight and energy stored in a lead acid battery remained much as in 1890! Whilst cheap and relatively simple, they were limited by their size and weight – providing about 34 Wh/kg.
In 1991, the USA launched its Advanced Battery Consortium. It was a US$90 million project, resulting in the nickel hydride (NiMH) battery. This initially doubled available energy to 68 Wh/kg – and has increases since then.
Early nickel hydride (NiMH) battery. Pic: ecomento.com
But whilst having greater energy density than lead acid batteries, NiMH’s have a low charging efficiency, high cost and a high rate of self-discharge (particularly when hot), plus the need to control hydrogen loss. Despite this they have successfully powered most hybrid electric vehicles (including Honda and Toyota) for a now 20 years.
In 1996, the University of Texas conceived the lithium-ion battery. (At a now (140 Wh/kg) these batteries store more energy than their NiMH equivalents, can be charged at a far higher rate and able to release huge amounts of energy over a short time. As of 2019, these batteries provide electric-only cars with a realistic range of 250-450 km (dependent also on speed) between charges. Whilst detractors see this as borderline it is adequate for urban commuter driving – not least as they can readily be topped up overnight from home grid power – see Solar Charging Your Electric Car.
Whilst lithium-ion batteries have high energy density they are costly to make –and done so via an emissions producing process. There is also ongoing concern of their catching on fire. Despite this, ongoing efforts are underway to increase lithium-ion storage capacity. That most feasible is the use of graphene.
Graphene is virtually two-dimensional. It is literally one atom thick (the height of three million layers is 1.0 mm). Each graphene-layer consists of hexagonal honeycomb-like rings in which the atoms are intensely strongly co-bonded. Graphene is ultra-strong, has next no electrical resistance and is an extraordinary conductor of heat. The material enables lithium-ion batteries to increase their capacity per kg. By replacing the carbon currently needed to for internal conductivity graphene it enables them to charge faster, and increases battery life.
The graphene one atom thick lattice. Pic: Original source unknown
Right now, graphene-based batteries are not yet commercially available but research and development is intensive. As noted below, there are also ongoing efforts into producing batteries using other than lithium ion.
Ultracapacitors store energy in a liquid between an electrode and an electrolyte. They can release this energy at ultra-high rate, assisting acceleration and hill climbing. They can also store regenerative braking energy.
An ultracapacitor. Pic: Maxwell Technologies
They are also likely to be used as secondary energy-storage devices in electric vehicles because they help electrochemical batteries to level load power.
Alternative battery technologies
A possible breakthrough may have been made by Piëch Automotive’s electric car, powered by an all-new battery claimed to recharge to 80% in less than five minutes.
The Piech Automotive electric car. Pic: Piech.
The company states that: ‘Significantly higher currents can flow as the cell temperature rises only marginally…. the fast charging mode allows for a sensationally short charging time of only 4:40 minutes to 80% battery capacity with an exceptionally high recuperation rate. Because of the reduced heat build-up, the batteries can be cooled by air alone.’ The company claims such cooling saves 200 kg.The vehicle has three electric motors: one front-axle asynchronous motor which delivers 150 kW, and two rear-axle synchronous motors to produce 150 kW each. Its range is claimed to be 500 km – using the EU’s new WLTP cycle.
The WLPT (Worldwide Harmonised Light Vehicle Test Procedure) is a new test procedure based on global real-life driving data. It takes in low, medium, high and extra high speeds, and a variety of stops, acceleration and braking phases. Each vehicle is tested to reveal its most economical and least economical modes.
Electric vehicle battery life
Battery technology is now such that sudden failure after some years is very rare. Because of this, most battery makers quote a lifespan based on the number of charge/discharge cycles that reduces the battery’s original capacity to 80%. It may still be usable – but 20% of its capacity is lost.
Battery life also substantially depends substantially on their routine depth of discharge. Those used in electric car used mostly for urban driving and fully charged each night will long outlast those deeply discharged on frequent long drives.
Right now (early 2019) most electric car makers guarantee the batteries for eight years. Nissan, for example, guarantee them against defects for eight years or 160,000 km, and capacity loss for 5 years or 96,500 km. Outright failure however is improbable so owners can run them longer if they can cope with a shorter distance between charges.
Some years ago, the originally Israeli-based company Phinergy (in conjunction with Alcoa) developed a non-rechargeable ‘battery’ enabling a claimed range of 1600 km for small to medium sized electric vehicles. It works by energy being released via a reaction of aluminium and water when mixed with oxygen (from the air) using a silver-based catalyst.
The Phinergy ‘battery’. Pic: Phinergy
Aluminium has electrical potential and Phinergy’s product is claimed to release electricity in a process that is the reverse of its original smelting. Each ‘battery’ is claimed to extract 8.1 kilowatt-hours of energy (50% electricity and 50% heat) per kg of aluminium. When fully depleted the battery is replaced.
Phinergy recently stated that it is now associated with the Indian Oil Corporation and that Ashok Leyland is involved. The concept seems interesting but would seem to need wide acceptance to set up to service the replacement requirements.
The potential market is huge for quickly rechargeable batteries that are light and compact. One or another will eventually evolve: when electric-only vehicles are likely to have a range that is all but unthinkable for fossil-fuels. In the meantime, hybrid vehicles are an excellent compromise. See also Electric Vehicles – Hybrids.