Electric car charging methods

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Electric car charging at National Air and Space Museum, 12 December 2016. Electric car charging 125912.jpg
Electric car charging at National Air and Space Museum, 12 December 2016.

Various methods exist for recharging the batteries of electric cars. Currently, the largest concern surrounding electric vehicle transportation is the total travel range available before the need to recharge. The longest range recorded till date was 606.2 miles, achieved by a Tesla Model 3. However, this was conducted in very controlled conditions where the car maintained a constant speed without the added drain of the air conditioning compressor. [1] Typically, the battery would last for approximately 300 miles - the equivalent to three days of city commuting in warmer weather, or one day in colder weather. With these limitations, long-distance trips are currently unsuited for an electric car unless rapid charging stations are available on the route of the trip.

Contents

Principles of rapid charging

Chassis of a Tesla Model S, exposing battery pack area Tesla Model S subframe front 02.jpg
Chassis of a Tesla Model S, exposing battery pack area

The process of discharging involves lithium ions from a positive electrode passing through a separator/electrolyte. The ions then transfer, via a solid electrolyte interface (SEI) and intercalate, into the negative electrode. The potential negative impact for rapid charging is that battery aging may be accelerated by the unstable SEI, produced by charging and discharging multiple times.

New pulse charging has significantly improved the stability of SEI since the unnecessary chemical reaction has been reduced by new charging methods and SEI is grown via a reduction reaction. Thus, a battery's life cycle and efficiency has also improved in comparison to the traditional charging method. [2] Also, in traditional charging method, ethylene might be produced during charging due to electrolyte (EC, mostly) reduction with lithium ions. Since the battery is closed, the internal pressure is contained. The produced ethylene will lead to overpressure inside the battery. Overpressure of the battery may also cause the battery to expand due to an internal temperature rise, potentially causing the battery to explode. By using these new composite waveform charging method, however, it can reduce the produced ethylene by suppressing the electrolyte reduction reaction. Therefore, giving a moderate energy for lithium ions to transfer during charging and a quick negative pulse to reduce unwanted chemical reactions, it seems to be a theoretical charging method in the future. [3]

Charging algorithms

The different algorithms vary in charging efficiency, charging time, battery life cycles, and costs. However, researchers still cannot define which is the most appropriate one for the application, as many algorithms have been developed; each one has advantages and disadvantages. For instance, the constant current-constant voltage charging method has a longer charging time compared to the multistage current charging algorithm, while the cost of research on the latter is higher than the former. Considering the pros and cons of each algorithm, the goal is to match each one with its appropriate application.

Constant current

The constant current charging method adjusts the output voltage of charging devices or the resistance in series with the battery to keep the current constant. It uses a constant current value form the beginning to the end of charging. As nickel-cadmium batteries are easy to polarize during conventional charging, the electrolyte continuously produces hydrogen-oxygen gas in both conventional constant voltage and constant current charging algorithms. Under the action of internal high pressure, the oxygen penetrates to the negative electrode and interacts with the cadmium plate to generate CdO, resulting in the decrease of effective capacity of the electrode plate. As the acceptable current capacity of the battery decreases gradually with the progress of the charging process, this led to the overcharging of the battery in the later charging period. Eventually, it will also lead to a sharp drop in battery capacity. [4]

Constant voltage

Constant voltage charging is a widely used charging method involving constant voltage between the battery poles. The starter battery uses constant voltage charging when the vehicle is running. If the specified voltage constant value is appropriate, it can ensure that the battery is fully charged, while also minimizing gas and water loss.

Variation of constant current/constant voltage charging algorithms

The boost charger CC/CV charging algorithm is a further development of the constant current/constant voltage algorithms. Instead of using the constant voltage and current in the entire charging period, it boosts the charging efficiency through maximizing voltage in the first period, with the battery reaching approximately 30% of its nominal charging capacity. After this period, the charging algorithm is then switched to the standard CC/CV. [5] Due to the initial higher charging voltage, the BC-CC/CV can charge the battery faster than the CC/CV, but it is required to fully discharge the battery before charging. As the charger needs to provide variable voltage, all components need to accept the highest voltage generated by the boost charger. Discharging the battery before recharging is important as this will influence the efficiency charging algorithm and the life cycle of batteries.

Multistage current charging algorithm

Multistage current charging divides the entire charging period into several charging stages that attempt to use the optimal charging current across each stage, maximize the charging efficiency. By determining the optimal charging current for each stage, the fuzzy controller is used to determine the charging current by the change in temperature. To sum up, this algorithm is based on a micro-controller or a computer. [6] The charging speed is faster and charging efficiency is higher than those of the CC/CV.

Non-contact charging method

Wireless charging

Non-contact charging utilizes magnetic resonance to transfer energy in the air between the charger and battery. This achieves a highly efficient energy transformation. [7] As the non-contact charger could keeping charging the vehicle, it allows EVs to have a smaller battery. By itself, it is more economical, safer and more sustainably developed. Since the battery is the major contributor to the cost of an EV, the MSRP of an EV is lowered as a result of the use of non-contact charging. However, developing a non-contact charging system involves huge financial support. For example, to realize real-time charging on the road, it requires installation of receiver coil under the car and reconstruct the road and put transmitter coil under the power supply track. In this way, it allows car to be automatically charged while operating on the road. [8] Due to this, many EV manufacturers are using traditional charging methods to keep costs low. Since non-contact charging systems rely on the electromagnetic field as their mechanism of action, electronic devices in close proximity to the charger may be negatively affected during charging. There is also the possibility that animals may be influenced. Efficiency is another concern for researchers.

Battery swap

Battery swapping involves the use of an automatic or semi-automatic system to exchange a depleted battery with a fully charged one. [9] This process can only be completed by technical personnel. The process is meant to achieve a comparable refuelling time to a traditional gasoline vehicle, with swaps typically completed in roughly 3 minutes.

On-board solar charging

Related Research Articles

<span class="mw-page-title-main">Electrode</span> Electrical conductor used to make contact with nonmetallic parts of a circuit

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. Electrodes are essential parts of batteries that can consist of a variety of materials depending on the type of battery.

<span class="mw-page-title-main">Electrochemical cell</span> Electro-chemical device

An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells. A common example of a galvanic cell is a standard 1.5 volt cell meant for consumer use. A battery consists of one or more cells, connected in parallel, series or series-and-parallel pattern.

<span class="mw-page-title-main">Nickel–metal hydride battery</span> Type of rechargeable battery

A nickel metal hydride battery is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although much less than lithium-ion batteries.

<span class="mw-page-title-main">Nickel–cadmium battery</span> Type of rechargeable battery

The nickel–cadmium battery is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation Ni-Cd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all Ni–Cd batteries.

<span class="mw-page-title-main">Lithium-ion battery</span> Rechargeable battery type

A Lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees significant use for grid-scale energy storage and military and aerospace applications. Compared to other rechargeable battery technologies, Li-ion batteries have high energy densities, low self-discharge, and no memory effect.

<span class="mw-page-title-main">Rechargeable battery</span> Type of electrical battery

A rechargeable battery, storage battery, or secondary cell, is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or primary battery, which is supplied fully charged and discarded after use. It is composed of one or more electrochemical cells. The term "accumulator" is used as it accumulates and stores energy through a reversible electrochemical reaction. Rechargeable batteries are produced in many different shapes and sizes, ranging from button cells to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of electrode materials and electrolytes are used, including lead–acid, zinc–air, nickel–cadmium (NiCd), nickel–metal hydride (NiMH), lithium-ion (Li-ion), lithium iron phosphate (LiFePO4), and lithium-ion polymer.

<span class="mw-page-title-main">Lithium polymer battery</span> Lithium-ion battery using a polymer electrolyte

A lithium polymer battery, or more correctly lithium-ion polymer battery, is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. High conductivity semisolid (gel) polymers form this electrolyte. These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, such as mobile devices, radio-controlled aircraft and some electric vehicles.

<span class="mw-page-title-main">Internal resistance</span>

A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This impedance is termed the internal resistance of the source. When the power source delivers current, the measured voltage output is lower than the no-load voltage; the difference is the voltage drop caused by the internal resistance. The concept of internal resistance applies to all kinds of electrical sources and is useful for analyzing many types of electrical circuits.

<span class="mw-page-title-main">Battery charger</span> Device used to provide electricity

A battery charger, or recharger, is a device that stores energy in a battery by running an electric current through it. The charging protocol depends on the size and type of the battery being charged. Some battery types have high tolerance for overcharging and can be recharged by connection to a constant voltage source or a constant current source, depending on battery type. Simple chargers of this type must be manually disconnected at the end of the charge cycle. Other battery types use a timer to cut off when charging should be complete. Other battery types cannot withstand over-charging, becoming damaged, over heating or even exploding. The charger may have temperature or voltage sensing circuits and a microprocessor controller to safely adjust the charging current and voltage, determine the state of charge, and cut off at the end of charge.

<span class="mw-page-title-main">Molten-salt battery</span> Type of battery that uses molten salts

Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehicles and for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.

A polymer-based battery uses organic materials instead of bulk metals to form a battery. Currently accepted metal-based batteries pose many challenges due to limited resources, negative environmental impact, and the approaching limit of progress. Redox active polymers are attractive options for electrodes in batteries due to their synthetic availability, high-capacity, flexibility, light weight, low cost, and low toxicity. Recent studies have explored how to increase efficiency and reduce challenges to push polymeric active materials further towards practicality in batteries. Many types of polymers are being explored, including conductive, non-conductive, and radical polymers. Batteries with a combination of electrodes are easier to test and compare to current metal-based batteries, however batteries with both a polymer cathode and anode are also a current research focus. Polymer-based batteries, including metal/polymer electrode combinations, should be distinguished from metal-polymer batteries, such as a lithium polymer battery, which most often involve a polymeric electrolyte, as opposed to polymeric active materials.

<span class="mw-page-title-main">Nanobatteries</span> Type of battery

Nanobatteries are fabricated batteries employing technology at the nanoscale, particles that measure less than 100 nanometers or 10−7 meters. These batteries may be nano in size or may use nanotechnology in a macro scale battery. Nanoscale batteries can be combined to function as a macrobattery such as within a nanopore battery.

<span class="mw-page-title-main">Lithium-ion capacitor</span> Hybrid type of capacitor

A lithium-ion capacitor (LIC) is a hybrid type of capacitor classified as a type of supercapacitor. It is called a hybrid because the anode is the same as those used in lithium-ion batteries and the cathode is the same as those used in supercapacitors. Activated carbon is typically used as the cathode. The anode of the LIC consists of carbon material which is often pre-doped with lithium ions. This pre-doping process lowers the potential of the anode and allows a relatively high output voltage compared to other supercapacitors.

Rechargeable lithium metal batteries are secondary lithium metal batteries. They have metallic lithium as a negative electrode, sometimes referred to as the battery anode. The high specific capacity of lithium metal, very low redox potential and low density make it the ideal anode material for high energy density battery technologies. Rechargeable lithium metal batteries can have a long run time due to the high charge density of lithium. Several companies and many academic research groups are currently researching and developing rechargeable lithium metal batteries as they are considered a leading pathway for development beyond lithium-ion batteries. Some rechargeable lithium metal batteries employ a liquid electrolyte and some employ a solid-state electrolyte.

<span class="mw-page-title-main">Electric battery</span> Source of stored electrical energy consisting of one or more chemical cells

An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices.

The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.

<span class="mw-page-title-main">Supercapacitor</span> Electrochemical capacitor

A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor with a capacitance value much higher than other capacitors, but with lower voltage limits, that bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than rechargeable batteries.

A dual carbon battery is one that uses carbon for both the cathode and the anode.

Lithium–silicon battery is a name used for a subclass of lithium-ion battery technology that employs a silicon-based anode and lithium ions as the charge carriers. Silicon based materials generally have a much larger specific capacity, for example 3600 mAh/g for pristine silicon, relative to graphite, which is limited to a maximum theoretical capacity of 372 mAh/g for the fully lithiated state LiC6. Silicon's large volume change (approximately 400% based on crystallographic densities) when lithium is inserted is one of the main obstacles along with high reactivity in the charged state to commercializing this type of anode. Commercial battery anodes may have small amounts of silicon, boosting their performance slightly. The amounts are closely held trade secrets, limited as of 2018 to at most 10% of the anode. Lithium-silicon batteries also include cell configurations where Si is in compounds that may at low voltage store lithium by a displacement reaction, including silicon oxycarbide, silicon monoxide or silicon nitride.

An aqueous lithium-ion battery is a lithium-ion battery (Li-ion) that uses a concentrated saline solution as an electrolyte to facilitate the transfer of lithium ions between electrodes and induce an electrical current. In contrast to non-aqueous lithium-ion batteries, aqueous Li-ion batteries are nonflammable and do not pose any significant risks of explosion, because of the water-based nature of their electrolyte. They also lack the poisonous chemicals and environmental risks associated with their non-aqueous counterparts.

References

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