By Stephen Evanczuk
For circuits relying on lithium-ion cells, determining the amount of charge remaining in a cell requires specialized techniques that can complicate the design of energy-harvesting applications. Engineers can implement these techniques with MCUs and ADCs normally used in these applications, but at the cost of increased complexity. Instead, engineers can easily add this functionality to existing designs using dedicated “fuel-gauge” ICs available from manufacturers including Linear Technology, Maxim Integrated, STMicroelectronics, and Texas Instruments.
Determining the state of charge (SOC) in lithium-ion batteries is essential yet challenging due to the great variability in capacity not only across different cells, but also in the same cell. As a Li-ion cell ages, it loses its ability to store charge. Consequently, even if fully charged, an older cell would deliver usable voltage for a shorter period of time than a newer cell. With any Li-ion cell, SOC varies greatly depending on the temperature and discharge rate, resulting in a unique family of curves for any particular cell (Figure 1).
Fuel-Gauge ICs Simplify Li-Ion Cell Charge Monitoring - [Link]
The weak link in electric vehicle technology is the method of energy storage and renewal, making the vehicles impractical for long distance use. The majority of today’s electric vehicles use rechargeable lithium-ion batteries which still have a relatively poor energy density compared to conventional fossil fuels and require lengthy recharge cycles. A promising alternative battery chemistry is the lithium-sulfur battery. It can store as much as four times more energy per mass than lithium-ion batteries.
Unfortunately reactions at the battery’s sulfur-containing cathode form molecules called polysulfides that dissolve into the battery’s electrolyte. The dissolved sulfur eventually develops into a thin film called a solid-state electrolyte interface layer which coats the lithium-containing anode making the battery unusable after only 100 charge/discharge cycles.
Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have succeeded in quadrupling the useful number of charge/discharge cycles. They have developed a graphite shield which moves the sulfur side reactions away from the anode’s lithium surface, preventing it from growing the debilitating interference layer. The new hybrid anode combines graphite from lithium-ion batteries with lithium from conventional lithium-sulfur batteries.
Graphite Boosts Battery Life - [Link]
By Ashok Bindra,
Over the years, demand for efficient, light, fast-charging, safe, and cost-effective portable power has led to development of many new battery technologies, including nickel-metal hydride (NiMH), rechargeable alkaline, lithium-ion (Li-ion), and lithium-polymer (Li-poly), to name a few. Generally speaking, these new battery chemistries require more sophisticated charging and protection circuitry to maximize performance and ensure safety. Fortunately, equally advanced semiconductor devices to charge and protect them have also been developed.
This article explores the virtues and limitations of the newer battery technologies. It also investigates and reports on new charging solutions for Li-ion batteries from semiconductor suppliers like Maxim Integrated, Linear Technology, and Texas Instruments.
New Battery Charging Solutions for Li-ion Cells - [Link]
By Steven Keeping:
Power management in portable devices is one of the toughest challenges faced by electronic engineers. The consumer demands instant response from their device, lots of functionality, and a large, bright and colorful touchscreen. Moreover, many of these portable devices now incorporate wireless connectivity that places further demand on the cell. And yet, the user expects the battery, a sensitive lithium ion (Li-ion) cell that requires careful recharging from a number of sources including USB sockets, to last for at least a day and then refresh quickly.
Designing a power management system to meet these conflicting problems is tough. However, there are some proven design techniques that help extend battery life. Moreover, the key semiconductor vendors have made life a little easier by offering power management units (PMUs) that integrate some, or even all, of the functionality needed for the efficient power supply of portable devices.
Design Techniques for Extending Li-Ion Battery Life - [Link]
This application note describes how to recycle lithium-ion (Li+) batteries from older devices for use in other electronic devices, such as toys. This can all be done without the need for a microcontroller (or the required software). One challenge is that the battery charger in these older devices cannot usually be reused. The designer needs to create their own charger circuit, which this application note explains how to do in detail.
Lithium-Ion Battery Recycling Made Easy - [Link]
This collection of circuits provides step-up voltage regulation for single cell and dual cell Alkaline, NiMH, and Li+ battery driven applications. Regulate your battery driven app with an efficient converter from Maxim.
Your battery-powered application needs regulation. This collection of circuits provides step-up voltage regulation for single- and dual-cell Alkaline, NiMH, and Li+ battery-driven applications.
A simple 1A step-up converter in a tiny WLP package that can be used in any single-cell Li-ion application. This IC provides protection features such as input undervoltage lockout, short circuit, and overtemperature shutdown.
The input voltage of these circuits range from 0.7V to VOUT and they have a preset, pin-selectable output for 5V or 3.3V. The outputs can also be adjusted to other voltages using two external resistors.
MIT has designed an ultra-low cost “flow” battery that it claims will store 10-times as much energy as lithium-ion while consuming 10,000 times less power, making it a candidate to meet the Department of Energy’s target of less than $100 per kilowatt-hour for grid-scale deployment. [via]
MIT’s flow battery simplifies rechargeable technology by eliminating the ion-exchange membranes. The lower solid graphite electrode reduces liquid bromine to hydrobromic acid, while hydrogen is oxidized at the upper porous electrode.
Flow Batteries Go Mainstream - [Link]
A team at the University of Illinois has unveiled a battery design which offers 10 times the energy density and 1000 times faster recharge time compared to current cell technology according to a paper in the Journal Nature Communications.
The battery uses a LiMnO2 cathode and NiSn anode but the real innovation is in the novel electrode design. The electrodes are fabricated using a lattice of tiny polystyrene spheres which are coated with metal. The spheres are then dissolved to leave a 3D-metal scaffold onto which a nickel-tin alloy is added to form the anode, and the mineral manganese oxyhydroxide forms the cathode. In the last stage the glass surface is immersed into a liquid heated to 300˚C (572˚F). The resulting structure massively increases the electrode surface area and reduces the clearance between the electrodes. [via]
New Battery Technology Charges 1000 Times Faster - [Link]
Fritz Weld writes:
Lithium-ion batteries are sensitive to bad treatment. Fire, explosions, and other hazardous condition may occur when you charge the cell below the margin that the manufacturer defines. Modern battery chargers can manage the hazardous conditions and deny operation when illegal situations occur. This fact doesn’t mean, however, that all cells are bad. In most cases, you can replace the discharged battery and increase your device’s lifetime. Figure 1 shows the circuit for testing battery packs.
Simple circuit indicates health of lithium-ion batteries - [Link]
Peter T Miller writes:
Like other simple, single-cell lithium-ion battery chargers, Microchip’s MCP73812 provides no means of indicating the charging status. You can remedy this situation by adding four components (Figure 1). Add one more LED, and you also get a charging-complete indication. This two-LED configuration has the added benefit that one of the LEDs is always on, providing an indication that the charger is powered.
Add charging status to simple lithium-ion charger - [Link]