The Importance of Safety and Performance of Lithium-ion Batteries

Table of Contents

Introduction
How Lithium-Ion Batteries Work
Introduction: Growing Demand for Lithium-Ion Batteries
Critical Issue: Improving Performance
Critical Issue: Addressing Safety Concerns

Introduction

Lithium-ion batteries are lightweight and provide efficient power for consumer electronics and electric vehicles (EV). The future of lithium-ion batteries is bright as they provide higher energy density when compared to other types of rechargeable batteries, but nevertheless two critical issues that have to be addressed are safety and performance.

In EV applications, issues like deterioration of battery over time and limited driving range make EVs less appealing for consumers. Therefore, performance is particularly significant for such applications. Safety is also a major concern. There have been reports of battery fires in EVs and smartphones and these have brought the focus on consumer safety issues.

While application or systems Engineers choosing batteries for use in end products are aware of footprint and voltage requirements, they may not be familiar with failure mechanisms or battery chemistry. This article provides information that may help those Engineers to ask the right types of questions to potential suppliers, and thus improve the odds that their product contains a battery that is optimized for their particular application.

The article also provides a basis to learn more about lithium-ion batteries, with a focus on information that will be useful to Systems or Application Engineers tasked with battery selection. The information is also helpful to Battery Designers and provides them a better understanding on how to effectively work with customers. Finally, the article shows why batteries should be properly characterized to improve performance and address safety issues.

How Lithium-Ion Batteries Work

An overview is first provided about the workings of lithium-ion batteries, discussing trends in battery materials and battery chemistry. Explanations are also provided on what can go wrong. Many different issues can play a role in the degradation or failure of batteries, and understanding the cause of failure is also highly complicated.

A range of in-situ and destructive characterization techniques, along with examples of failure analysis applications, are also described here. Engineers can use this information to choose a suitable battery characterization technique and also know the type of questions to ask when they work with an independent testing facility. Techniques for both chemical analysis and imaging are also covered. When performing destructive analysis, proper battery disassembly procedures should be followed. This article provides a brief summary of issues to be aware of, highlighting the requirement for properly trained workers.

Introduction: Growing Demand for Lithium-Ion Batteries

As mentioned before, lithium-ion batteries are lightweight and provide higher energy density when compared to nickel–metal hydride (NiMH) or lead-acid batteries. As a result, there is a huge demand for lithium-ion batteries in electric vehicles (EV), consumer electronics and energy storage. Lithium-ion batteries, compared to NiMH batteries, have a 50% greater capacity in watt-hours per kilogram (w-h/kg).

There is a huge demand for higher-efficiency batteries in the EV industry, and Vehicle Manufacturers in response are increasing the production of lithium-ion battery production. For instance:

  • Tesla is constructing a “gigafactory” in Nevada that is claimed to generate sufficient lithium-ion batteries to support its scheduled production rate of 500,000 cars per annum by 2020.1
  • Lithium-ion batteries are present in all commercial EVs as well as plug-in hybrid vehicles. Currently, 18 Manufacturers are marketing plug-in or electric models and more models are expected to come in 20172. This is indeed an encouraging market for Battery Manufacturers.
  • Toyota’s higher-end Prius hybrid vehicles include lithium-ion batteries, enabling those cars to attain the same mileage as more-stripped-down models with NiMH batteries, although they include options that add extra weight.3

Critical Issue: Improving Performance

In spite of their various benefits, lithium-ion batteries come with certain challenges that may delay their widespread adoption. Operating life and total life span continue to be the main problems

Today’s batteries have greater operating life between charges when compared to the older designs, but there is still room for improvement, particularly for EV applications. Even when running complex applications, batteries in mobile phones can last for one whole day before they need charging, and this is adequate for most consumers.

When batteries have to be charged, an outlet can be easily located and the phone can be charged within an hour. Although EV range is improving, it is restricted to 100 miles or less on a majority of vehicles. Also, charging stations are not always easily located. It takes many hours to charge a depleted battery with standard level 2 chargers, making them impractical for drivers needing to travel long distances.

Lithium-ion battery performance can degrade over a period of time, at a rate that relies on the design and materials of the batteries as well as end use. Multiple reasons can degrade the performance of batteries, as illustrated in the “Common Battery Failures” section of this article. Laptops and mobile phones make use of lithium-ion batteries that last only for a few years and after this period they will not be able to hold a charge. Lithium-ion batteries used in EVs should be much more robust, and many come with 100,000 mile and 8 to 10 year warranties. Even then, charging capacity tends to decrease over that period, further decreasing the car’s resale value.

Critical Issue: Addressing Safety Concerns

Earlier in September 2016, the recall of Samsung Galaxy Note 7 phones again highlighted the safety concerns with regard to lithium-ion batteries. At first, Samsung believed the reason was a manufacturing defect from a specific third-party battery supplier that caused the devices to catch fire. The company went on to provide customers with free replacement batteries from another supplier. However, when phones containing the replacement batteries again caught fire, Samsung responded by stopping the development of all Galaxy Note 7 mobile phones in October.

As of January 2017, almost all the three million Note 7 cell phones sold worldwide have been returned to the company. The Samsung story underlines the significance of developing batteries keeping the end application in mind and performing routine and thorough system-level tests. Although Samsung continues to blame the design of the battery, the footprint and power demands of that particular phone could also have played a contributing role.

There were a number of dramatic incidents that involved Tesla cars, during which the cars were fully consumed by flames within a matter of minutes, after a battery fire started. These incidents reiterate the importance of the reliability of lithium-ion batteries. To deal with this issue, Tesla re-modeled its S vehicles in 2014 adding aluminum and titanium underbody shielding so that the battery pack does not attract the road debris.4 However, in spite of this measure, two Model S vehicles still caught fire in 2016.5,6

When compared to other types of batteries, lithium-ion batteries are more likely to catch fire. Although, the number of battery fires is very small compared to the number of batteries in service, the risk of fire should be significantly reduced so that consumers are confident about the safety of lithium-ion batteries. The prospect of an EV catching fire is frightening.

Fires occur when shorts between the positive and negative electrodes cause the battery to heat up to an unsafe temperature. To better understand why lithium-ion batteries present a greater risk and how to reduce this risk, users should first understand the way lithium-ion batteries work and what can go wrong with them.

References

  1. “Tesla Gigafactory.” Tesla. www.tesla.com/gigafactory. Web. Accessed Sept. 26, 2016.
  2. “Cars.” Plugincars. http://www.plugincars.com/cars. Web. Accessed Oct. 4, 2016.
  3. M. Karkafiris, “This Is Why Toyota Offers Two Different Battery Options In The New Prius.” Car Scoops, Nov. 30, 2015. http://www.carscoops.com/2015/11/this-is-why-toyota-offers-two-different.html .
  4. E. Musk, “Tesla Adds Titanium Underbody Shield and Aluminum Deflector Plates to Model S.” Medium.com, March 28, 2014. https://medium.com/@teslamotors/tesla-adds-titanium-underbody-shield-and-aluminum-deflector-plates-to-model-s-544f35965a0d#.v3kkxea1j. Accessed Oct. 4, 2016.
  5. F. Lambert, “Tesla Model S catches on fire during a test drive in France.” Electrek, Aug. 15, 2016. https://electrek.co/2016/08/15/tesla-model-s-catches-fire-test-drive-france/. Web. Accessed Oct. 4, 2016.
  6. F. Lambert, “Tesla driver dies in a Model S after hitting a tree, battery caught fire, Tesla launches an investigation.” Electrek, Sept. 7, 2016. https://electrek.co/2016/09/07/tesla-driver-dies-burning-model-s-hitting-tree-tesla-investigation/. Web. Accessed Oct. 4, 2016.

This information has been sourced, reviewed and adapted from materials provided by Evans Analytical Group.

For more information on this source, please visit Evans Analytical Group.

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