Battery Chemistries for Electronic Products

Battery chemistry

When you go into the supermarket and buy batteries, you’re probably looking at two aspects: rechargeable vs. non-rechargeable. While this is obviously important for your electronic devices, the underlying chemistry determines the overall power handling capabilities and lifetime of a device. The chemistry needs to be chosen to provide the required power and lifetime for a device, and it is a bit more complex than choosing between a rechargeable vs. non-rechargeable battery.

In this article, we’ll look at some of the tradeoffs among various battery chemistries and the expected voltage, power, and discharge handling capabilities available in these systems. For small devices in the consumer electronics industry, it can be as simple as choosing between rechargeable vs. non-rechargeable battery chemistries. But for something like energy storage or electric vehicles,  the choice of battery chemistry and material set is critical for performance and safety.

Battery Chemistry and Performance

If you took a chemistry class in college or you’ve watched a video on battery chemistries, then you probably know something about how batteries operate. In general, the anode and cathode sides of a battery enable an electrochemical reaction on each end, which produces charge that can transfer between the battery terminals. A simple conceptual example of charge transfer can be found below.

Battery chemistry

The metals and separator material facilitate charge transfer in an electrochemical reaction, which produces a voltage between the anode and cathode.

In battery operation, there is a need to match up certain performance capabilities of a battery chemistry and system design with the needs of a particular system. For example, small mobile devices for consumers have seen a market trend of demand for increased lifetime. In contrast, in electric vehicles, discharge rate can take precedence when high power output is needed.

In addition, high discharge rate can cause the system to heat up significantly, so the construction of the battery system needs to be able to withstand heat generation without catching on fire. This might sound extreme, but in 2021, the US National Highway Traffic Safety Administration (NHTSA) opened an investigation into vehicle fires related to overheating batteries in electrified vehicles. The chemistry and system construction need to be matched to ensure performance and safety.

Battery Chemistries

The table below outlines the common chemistries used in primary and secondary cell batteries. These battery chemistries have been commercialized and are widely available for purchase.

Primary Cells

 

Alkaline

LiFeS2

LiMnO2

Ag2O

Voltage

~1.5 V

Up to 1.8 V

Up to 3.3 V

~1.5 V

Discharge

Low

Very high

Very low

Very low

Leakage

Very low

Low

Moderate

Low

Charge Density

Varies

High

High

Moderate

Cost

Low

Highest

Moderate

High

Secondary Cells

 

Pb-Acid

Ni-MH

Li-ion

Li-Po

Voltage

2.1 V

1.2 V

3.7 V

3.7 V

Discharge

Very high

Very high

Very high

Ultra-high

Leakage

High

Very high

Low

Low

Charge Density

Low

Moderate

High

High

Cost

Low

Moderate

Moderate

High

 

Selecting a chemistry requires balancing cost, charge density, discharge rate, and cost. Voltage is sometimes less important because battery cells can be stacked, and the voltage can be regulated down to a required value. Based on these factors, it is easy to see why Li-ion and LiPo (lithium-polymer) batteries have dominated when rechargeable devices are required.

In particular, when recharging is required in an end device, Li-ion is the best choice compared to Ni-MH (nickel metal hydride) batteries due to its much lower leakage and higher charge density. When very high discharge is needed, LiPo is arguably the best choice for rechargeable devices, although the tradeoff is higher cost.

Finally, we should note the use of Pb-acid batteries. Although one might assume that the use of these batteries was abandoned in the wake of the RoHS movement, these batteries account for approximately 70% of batteries used for renewable energy storage, and there are still more than 100 million of these batteries sold each year. Considering their high discharge rate and low cost, they are an acceptable battery system for certain applications.

Power Reduction in Embedded Devices

Increased feature density in modern electronics is pushing battery sizes and capacities to their limit. In today’s smartphones, the largest components are the screen, case, and battery. To slow down the need to keep increasing battery size, there are some methods to consider in system design for power consumption reduction. These include:

Beyond Standard Chemistries

There is significant research into alternative battery materials that intend to provide higher discharge rate, higher capacity, longer lifetime, and greater safety. There is also an environmental aspect as some research focuses on finding recyclable or biodegradable electrochemical materials for use in batteries. These battery materials are far from commercialization due to the challenges involved in proving safety, scaling manufacturing processes, and receiving regulatory approval for mass production and sale.

One of the leading alternative material classes for use in rechargeable batteries is carbon structures. Various carbon allotropes are being investigated for use as the primary electrochemical material in secondary cells, as a high-conductivity electrode material, or as separators in secondary cells. While an all-carbon battery is far-off and may never be commercialized, there is a lot of work looking at the use of unique carbon materials as electrodes in secondary cells.

Once you’re ready to select a battery chemistry for your system, make sure you use the complete set of system analysis tools from Cadence to build and evaluate the physical design of your system. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.

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