Where Do Lithium-Ion Batteries Stand in 2020?
Some of the leading players in Li-ion battery development—like Tesla—along with research universities are making notable strides in this energy-efficient technology.
The rise of small, portable electronics has demanded the concurrent development of powerful battery technology. Since the 1990s, lithium-ion batteries (Li-ion batteries or LIBs) have emerged as a frontrunner in the hardware arms race—usurping their nickel-based counterparts.
Flow of ions in a Li-ion battery. Image used courtesy of Battery University
Development cannot stagnate, however. We’ll explore what LIBS brings to the table, and why EEs working with R&D battery technology shouldn’t be complacent with LIB progress quite yet.
The Advantages of Lithium-Ion
Compared to metallic alternatives, lithium-ion is more stable during operation and while charging. Despite their lithium metal predecessors’ higher density, LIBs remain twice as energy-dense as nickel-cadmium batteries. They also have the following favorable characteristics:
- Single-cell construction and consolidation
- No memory or required charge scheduling for maintenance
- Slow discharge during rest
- Relatively-safe disposal
- Customizable cell configurations for diverse applications
Li-ion batteries outrank many other battery types in terms of specific energy density and volumetric energy density. Image used courtesy of Roberta A. DiLeo, Rochester Institute of Technology and the Clean Energy Institute
Li-ion technology generally retains an advantageous cost-energy ratio, although certain types of lithium-ion cells (prismatic slim) are more expensive. These batteries are also easy to replace while enjoying a long shelf life.
The Drawbacks of Li-ion
Compared to other technologies, Li-ion batteries tend to be weightier—underscoring the weight-power tradeoff in mobile devices. This partially fuels arguments over cell phone form factor. Many users prefer all-day (or multi-day) battery life, while others prefer ultimate portability. Some devices have grown increasingly large to accommodate cells with higher milliamp-hour (mAh) ratings. These deliver a longer service life between charges.
LIBs are user safe, yet require safeguards to stave off degradation during their lifespan. These protection circuits maintain voltage and current—keeping them stable. Li-ion technology still ages despite slow passive discharge.
Although a higher charge voltage can increase capacity, it can shorten the Li-ion battery's life cycle and decrease safety. Image used courtesy of Choi et al. and Battery University
Resource abundance is an ongoing question mark for lithium. Engineers primarily use the world’s 33rd most-abundant element for batteries. As far back as 2015, Green Tech Media reported that we only had enough global stores to last us 17 years in a worst-case scenario.
Lastly, battery shaping restricts internal component layouts. Engineers reliant on LIBs may have to adapt their chassis to accommodate them or make functional concessions. This hinders creative product design in some instances. It might also drive companies to source inferior alternatives. What have we done thus far to counter these shortcomings?
Innovations in Lithium-Ion Batteries in 2020
Some manufacturers have refused to accept the quirks of lithium-ion's form factor. With devices shrinking with each iteration, the onus has been placed on EEs to craft creative cell configurations.
Tesla’s Tabless Battery
One company that’s gone all-in on Li-ion technology is Tesla. The company has been refining its LIB technology since 2006 and has sought to mitigate existing Li-ion issues in creative ways. The company offers the following guidelines to prolong Li-ion battery life:
- Avoid extreme highs and lows in charge states (keeping cells constantly charged between 2% and 95%)
- Avoid rapid charging to promote energy stability and healthy internal temperatures
- Avoid charging in a cold state
- Avoid rapid discharge while limiting electrical current requirements per cell
Tesla has acknowledged that every battery will degrade over time. Serviceability thus becomes crucial for auto owners. Imagine if Tesla used a single-cell LIB for their vehicles. If that cell malfunctioned or died completely, a prohibitively-expensive repair would be needed. That’s why the company uses numerous cells (over 6,800 of them early on) in creating a single battery. Owners may have individual units replaced following degradation, instead of junking the car altogether.
In even more recent strides in battery technology, Tesla recently announced its tabless battery project to combat thermal gremlins and boost power output. These tabs are traditionally crucial in transferring power in large cells—while also lengthening the electrical path.
A cross-section of Tesla’s new tabless battery cell. Image used courtesy of Business Insider
This opens the door for heat generation while hampering performance. By removing tabs and instituting an internalized spiral matrix, it’s now possible to transfer power directly through the Li-ion material.
The critical electrical path is shortened, reducing operating temperature, promising five times more energy density, six times greater power, and 16% more range, according to Tesla. These types of advancements facilitate scaled production because the LIB design is simplified.
Stanford Suggests Solid Materials to Replace Liquid Electrolytes
A typical lithium-ion battery is composed of two electrodes with liquid electrolytes filling the space between. This liquid is volatile; punctures or shorts may cause ignition. Some manufacturers’ designs have been particularly susceptible. Note that a typical LIB includes a separator, which keeps the electrodes spaced apart while allowing energy transfer.
Diagram of a lithium-ion cell, including a separator and an ion flow between electrodes. Image used courtesy of Battery University
You might recall the spontaneous combustion debacle that plagued Samsung’s Galaxy Note 7; these device fires were ultimately caused by crimping, separator damage, and short-circuiting.
Stanford University researchers now suggest that solid materials could be worthy replacements for liquid electrolytes. They’re also more cost-effective.
Lithium, boron, and sulfur have risen to the top (thanks to machine learning screenings) as viable materials. Solids can withstand stress and resist breaking down for many more cycles, supporting the notion that solids can be conductive for much longer periods of time. Short-circuiting is also much less common.
The biggest challenges will be securing manufacturing pipelines and bridging the conductivity gap between liquids and solids.
South Dakota State University Champions Lithium Metal
It’s said that lithium metal is a holy grail in battery research. However, the long-term reliability of this material is questionable when used for anodes. The foil forms sharpened protrusions called dendrites over time. These dendrites can internally puncture the separator, thus causing shorts and fires.
The dendrites (pictured on the left) could break through separator material and cause short circuits and fires. Image used courtesy of Dean Sigler
What if we could stop dendrite growth in its tracks? Scientists at SDSU suggest that a new lithium-nitride coating between the anode and separator can do just that—negating the pitfalls of uneven lithium metal distribution.
The plasma-processed coating also promotes prolonged ionic conductivity during the battery’s lifespan. Lithium-metal batteries will accordingly enjoy greater popularity and even mechanical strength. They’ll also retain their capacity more effectively.
The Future of Lithium-Ion and its Cousins
It’s encouraging to see how far lithium-ion batteries have come since their inception. While the technology has achieved a degree of maturation, researchers are still finding ways to improve current technologies. Though many may suggest that battery development has slowed, the world’s foremost companies and universities are proving otherwise. We’re also finding new ways to make LIBs more economical during production.
That’s not to say that lithium-ion technology is the end-all-be-all. Global lithium reserves face a potential threat if development and consumption accelerate. Safety is vastly improved, and while battery failures are rare (under one in a million, according to Battery University), those failures can cause bodily or property damage.
Additionally, materials availability, cost savings, and eco-friendliness may soon thrust sodium-ion alternatives into the limelight.