Engineering Advances: Degradation and Saving Electric Vehicle Batteries

Degradation of EV Lithium Batteries 

Battery degradation in Electric Vehicles (See Figure 1. to Right) leads to capacity fade, thereby shortening the vehicle’s possible range.  Patterns are beginning to emerge and provide valuable insight into EV battery capacity and lifetime.  Most drivers are retaining over 90% of original capacity

Range Anxiety

Some cars have a range of only 106 miles, equivalent to just over three times the average daily drive in the US. New Electric Vehicles are expected to have a range of up to 235 miles, a 220% increase, therefore, range is constantly improving to address consumer concerns. Charging an EV takes time, and unless you have fast in-home charging infrastructure or public charging infrastructure it will remain a barrier.  Undoubtedly a point of address to boost EV adoption.

Are Lithium-ion Batteries the Preferred Choice?

Most of the EVs today run on lithium-ion batteries, the same technology that powers smartphones and laptops. Lithium-ion batteries have fallen in price by 80% in the last six years. However, an EV battery pack are still relatively expensive, some battery packs costs over $15,500 which makes up over 40% of the EV price.

Manufactures are following suit with their own battery factories, this ramp up in production will be the catalyst in bringing EVs into the market at competitive price points.

Fuel-cells (Fuel Cells )  (See Figure 2 Below) are similar to batteries in that they produce electricity without combustion or emissions. However, like gasoline vehicles, they can run for over 300 miles on one tank, and refuel within minutes While hydrogen fuel-cell is currently operating a fraction of market share, and lithium-ion batteries are the preferred choice, however, a desire exists to explore the opportunities in this technology.

It is not inconceivable to think that a few years down the line we are talking about a new battery compound, given the pace of technology.

There are challenges that EVs face before a material penetration can occur in the mass market. Developments in battery life, range, convenient charging, and competitive prices will be the catalyst in bringing EVs to the fore.

Fuel Cells 3

(Figure 2. Fuel Cells) 

Saving Your Battery 

Most electric vehicle batteries are lithium based. When a lithium battery is charged and discharged once, it is called a cycle. Lithium battery capacity degrades as the cycle number increases. (Battery) Cycle life is measured in cycles, with an industry standard of cycles to 80% capacity often used as a benchmark. What makes lithium batteries last a long time? Let’s turn that upside down. What shortens lithium battery life?

  1. High temperatures.Operating an EV in high temperatures can degrade the battery. Additionally, parking an EV in the sun for long periods of time can have similar degradation effects.
  2. Overcharging/high voltages.Charging an EV beyond its voltage limit can cause internal resistance in the battery. Most batteries have built-in battery management systems (BMS), so overcharging is rarely an issue, but it is good practice to not charge your battery right up to 100% when possible.
  3. Deep discharges/low voltages. Draining most of a battery’s capacity frequently, or completely draining an EV battery, reduces battery capacity over time.
  4. High discharges or charge current.Pulling too much current from a battery over a certain amount of time can have detrimental effects on battery life. When possible, avoid aggressive driving patterns that might pull high amounts of current from your battery all at once.

All EV Batteries (See Figure 3. Below) will degrade over time, but avoiding the above situations can help you maximize your EV battery life.

The idea is to avoid maximum voltage and high temperatures for extended periods of time. Battery manufacturers are aware of this, and keep their batteries at states of charge of as low as 40% to maintain battery capacity during storage and shipment.

Operating conditions can have a dramatic effect on battery performance and lifetime. Battery life must be assessed from both operating conditions and battery characteristics to accurately determine results. If you see claims from outsiders about the cycle life of a company’s batteries, be sure to find out if they have correct assumptions regarding temperature, maximum voltage or full charge, minimum voltage or depth of discharge, and C rate.

Conclusion: 

Electric Vehicles are going to need education on “best practices” for a long battery life. We will no longer have the “scheduled maintenance programs”, we have to have a “drive this way to avoid long term issues”.

 

(Figure 3. Electric Vehicle Battery) 

(Figure 1. Electric Vehicle)

2018-07-10T15:47:30+00:00

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