7th February 2020
Top 5 Challenges of Fast Charging For Electric Vehicles
Most electric vehicles (EVs) use lithium-ion batteries as their source of power. Lithium-ion batteries are rechargeable batteries that are typically used to power portable devices and electric vehicles (EVs) as well as hybrid electric vehicles (powered both by fuel and electricity). The batteries are considered fit for EVs due to their high power-to-weight ratio, high energy efficiency, good high-temperature performance, and low self-discharge. The idea of EVs is promising to address climate change by cutting down on carbon emission. EVs are being supported as the apparent substitute to fuel-powered cars; they are assured for a rapid growth phase with the blending outcome of longer range, lower battery cost and faster charging rate. However, the range and charging of EVs are still considerable concerns.
Fast charging is a decisive green light to the prevailing acceptance of EVs. It could be a solution to consumers’ range anxiety and the assurance of electric vehicles. The potential to recharge swiftly and efficiently is a critical demand for a storage battery. Likewise, a critical barrier to fast charging is temperature. To be truly competitive with gasoline vehicles, EVs should enable a driver to recharge swiftly parallel to gasoline-fueled vehicles. None of today’s EVs, however, grant fast charging in low temperatures. With this in mind, we are going to look at fast charging and its complications, so let’s get to it.
1. EVs and their fast-charging standards
Fast charging is viewed as tricky and organized technology. The mainstream power level of fast-charging EVs prescribes six to eight hours to score utterly charged batteries. Fast charging reduces the charging period to around thirty minutes. This ridiculous achievement comes stocked with some rules; EVs desire a source of AC and DC power to pump up their batteries. This source of power is oft-times supplied from a power grid. AC (Alternating-Current) chargers are typically found in workplaces or public areas and they allot 5kW to 12kW. DC (Direct-Current) chargers, on the other hand, can be found at studious EV charging terminal, such as Tesla superchargers that often grant 50kW to 400kW or more. By contrast, DC fast chargers are the most possible power suppliers to hit a 30 minute charging period due to their high-power supply.
There are two known charging connector standards for EVs. There is the SAE J1772/ CCS which embodies both AC and DC charging into one connector. You might also come across the second connector known as CHAdeMO. It is considered as a fast-charging DC standard that supplies power ranging from 5kW to around 50kW at this time. The connector is known to support car brands like Toyota, Mitsubishi, Nissan, and Tesla (requires an adapter for compatibility). In this sense, not all connectors support all EVs or some EVs can only work with one connector specified by their manufacturer.
The major problem, as it turns out, most chargers today are proved to be “level 2,” meaning that they deliver 6 to 18kW per hour (equivalent to gallons of gas). It would take approximately eight hours to top up a pure EV with a typical Level 2 charger. The solution to this problem would be to install direct-current fast chargers to significantly slim the charging time. Charging takes planning, you have to know the specifics of the car you are driving and be aware of a charger’s capability when you are in public.
However, the use of DC fast chargers requires electrical infrastructure adopted for high power, and these chargers do not come cheap. The increased voltage will require additional insulation, which may add volume and mass to the electrical components, cables, and connectors of the vehicle. A higher battery voltage will also require a pack with more cells aligned in series. This will require more sensing and balancing circuits to monitor and balance the battery pack so as to meet the low resistance requirements for high-accuracy measurements.
2. Battery technology gap and Lithium plating
Fast charging is known to cause lithium-plating which happens in cold temperatures when lithium deposits form around the anode of the battery during charging; it deteriorates battery life and safety. In regards to Xiao-Guang Yang, Pennsylvania State University, efforts to enable fast charging are prevented by the nature of lithium-ion batteries. He continues and says that improving low-temperature fast-charging capability usually sacrifices cell durability.
Yang and his team then present a controllable cell structure that breaks the nature of a lithium-ion battery by enabling lithium plating-free fast charging. This technique helps promote the uniform charging practice regardless of ambient temperature.
In practice, this offers the development of battery materials with no temperature restrictions. This could make fast charging truly weather-independent. But the team is not done yet. They are looking at what kind of materials they might need to fully charge an EV battery in just five minutes. The kind of charging speeds you wouldn’t rather do anything else other than watch your EV top-up.
Passive Cell Balancing
The newest lithium-ion batteries with graphite anodes and flux metal oxide cathodes in liquid electrolytes are unfit to clinch fast-charging ambition without upsetting electrochemical performance and safety. It is easy for graphite to produce lithium plating since the insertion of lithium into graphite occurs within a very narrow potential range that is close to the thermodynamic potential of the lithium ions.
The effective detection of lithium plating to avoid the thermal pathway of the battery is a necessary measure to ensure the safe operation of batteries. Substantial research has been overseen on the greater expanse development of lithium-ion batteries; change in cell thickness is also a nondestructive detection indicator of lithium plating. Beholding lithium plating and the context in which it is likely to occur is crucial to make good headway in fast charge-capable vehicle adoption.
It is emphasized that to essentially solve the problem of fast charging, the development of new anode materials with improved lithium-ion diffusion coefficients, is the way forward. Researchers are zeroing in on red phosphorous which to be the most promising anode that can simultaneously satisfy the double standards of high-energy-density and fast-charging performance to a maximum degree.
3. Thermal management systems
Temperature and humidity levels highly affect the performance, safety, and lifetime of battery cells, thus forging their dominance in a fundamentally provocative situation for battery integration into vehicles. We pointed out at the early stages of the article, the barrier between temperature and fast charging. As we now know lithium-ion batteries or rather, all batteries pivot on the electrochemical process whether charging or discharging and by some unspecified means, these chemical reactions hinge on temperature.
This is why thermal management systems are put in place to keep track of electrical (joule) heating and external thermal effects, where if the temperature is above the ambient temperature, the loss of heat could occur through conduction, convection, and radiation. When the ambient temperature is very high, then the thermal management system will perceive it inflexible to retain the temperature.
Excessive rise of temperature may cause the battery cell to swell, pressure may build inside the cell, gases may be given off, and the cell may ultimately breach or explode. Due to fast charging, all of this will come true and thermal management will tellingly procure a lot more important for the wholesale vehicle impression. When the battery temperature is too low or too high, the BMS alleviates the requested current to preserve the health of the battery cells. If the battery pack is equipped with a heating or cooling system the BMS will activate this system in order to control the cell temperature. Note that battery temperature is not only influenced by the outside temperature, but also by driving and charging as this will generally increase battery temperature.
4. Economic and infrastructure issues
Both the economic and infrastructure issues hindering the fruitful achievement of fast charging have technical hurdles that need to be addressed; access to charging infrastructure must improve. Fast charging at this timescale needs to materialize at a price that is sustainable to consumers, who rank not having enough access to efficient charging stations as the third most serious barrier to purchasing EVs. According to McKinsey’s 2016 EV consumer survey, charging could soon become the top barrier for possessing an EV especially now when EV prices are declining while ranges are expanding.
Unlike the Internal Combustion Engine (ICE) vehicles, which only refuel at gas stations, EVs are able to recharge at several locations in several ways. McKinsey’s model analyzes charging over four typical use cases that all support wired plug-in chargers: at home, at work, in public, and on highways. Home charging depends on whether EV owners have garages and on their income demographics. Charging at work commits to the employer’s choice or regulatory requirements.
Combined home, work, and long-distance charging could map an EV owner’s entire energy demand. In this case, drivers without chargers at home or work must charge in public places; drivers with an exceeded battery range on any day may need to visit fast-charge stations; and drivers who forget to charge at home or do not have home chargers are forced to bank on other courses of action, which later lead to public charging.
When it comes to economics, a familiar term comes into play, “Demand charges.” All electricity customers pay for the energy they consume, usually measured in kWh. In charging stations, customers also pay a demand charge for the maximum energy used in any period in a month. This energy, measured in kilowatts, is analyzed to redeem the fixed costs for power plants, power lines, and transformers that connect customers to the grid and supply power even when there are high demands. As soon as a car plugs in, the station owner must pay a demand charge, and those charges go up for drivers, too. This is based on the number of chargers on the station, the maximum power in kilowatts, consumed by the car when plugged in, and the number of cars charging simultaneously in any 15 to 30-minute segments.
The key analysis for economic and infrastructure success for fast charging includes grid stability and remittance of power, the design of fast charging stations and the design and use of electric vehicle service bits and pieces. The excellence of all these issues will positively impact the high power demand of fast charging and the cost of operation of charging infrastructure and EVs.
5. Convincing utility providers
As we move towards a renewable energy-powered world, convincing utility providers to change their business models will be a challenge. For EVs, the electrical energy needed for charging stations poses a problem for utility providers. If that is no problem enough, the providers will be obligated to contact each and every automaker who uses the charging station and inform them to quantify their electricity usage. This issue can only be resolved if all EV manufacturers merge to create a neutral platform, like a central server, so the utility providers only have to send one load reduction request. The manufacturer can respond accordingly, making it easier for all parties involved.
Now, we have seen that the techniques cast-off in fast-charging EVs have not yet lived up to the nitpicking standards predicted in scientific excellence today, which makes it complicated to draw definite conclusions. This article describes the current situations, problems, and development directions of fast charging technology for EVs, mainly referring to battery materials. None of the fast charging would be possible without the use of batteries, especially lithium-ion batteries.
The challenges faced by fast charging are as follows: model availability of EVs and their fast charging standards, battery technology gap including lithium plating, thermal management systems, economic and infrastructure issues promoted by demand charges, parking spaces and/ or charging stations; and the ability to convince utility providers to coordinate with all automakers. Lastly, it has been spotted that the essential way to solve this problem is to develop advanced electrode materials for fast-charging by improving the diffusion collective of lithium ions.
In practice, lithium-ion systems are often designed within the overall development process of the equipment with which they are interfaced, in close cooperation with OEM; or for systems in which the charging and operating conditions are broadly standardized. Designing a lithium-ion battery solution for any application should make an approach to selecting optimum electrochemistry, developing a battery system that meets the application requirements for performance, operating life, electrical and mechanic interfacing and safety, and testing and qualifying the specific operating conditions and abuse scenarios of the application. This development process inevitably means a slow but sure widespread adoption of lithium-ion technology.
For vehicles and infrastructure: It should be mentioned that new insulators to cope with high charging voltages and power semiconductors resistant to intense heat for charging stations should be emphasized and developed as quickly as possible. In future programs and in current programs outside those that we have discussed, energy companies should focus more on scientific research on electrochemical systems which prove to be packing potential long-term performance and cost criteria for EVs, as opposed to the development of systems based on existing science. Furthermore, the charging protocol of the major EV automakers should unify standards as soon as possible worldwide.
You should consider Batteries Electric Vehicles (BEVs) that meet the IEC 62133 safety standard and contain built-in protection circuitry. Do not allow BEVs to be overcharged or deeply discharged. Use manufactured battery cells; do not combine cells in series or parallel. Protect batteries from being broken down, ruptured, or short-circuited. Go ahead and get battery-specific information from the battery manufacturer about essential voltage, current, and temperature limits, before trying out fast-charging devices. The information, however, might be listed, in detail, on the battery pack or on the box that will have encapsulated the battery.
All things considered, it seems reasonable to assume that fast charging can be achieved through different approaches where other possibilities are yet to be uncovered. This puts into consideration that the rate at which a lithium-ion battery can be charged is still not fast enough. Above all, this process cannot be carefully thought of as successful without its assurance of safety and healthy battery life. Lithium-ion is a ‘squeaky clean’ system that only clutches what it can absorb; it is slowly charged to secure a complete electrochemical reaction.
It is time for you to decide on what it is that you want for your EV. Are you ready to benefit from fast-charging and at the same time risk leaving your battery or EV vulnerable to safety issues? Or are you willing to wait for a later time where fast charging will be safe for your EV and your battery?
To know more about improving battery life click here.
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