Tag Archives: rechargeable batteries

Protecting the Li-ion Battery

For decentralization of the source of energy, it is hard to beat rechargeable lithium-ion batteries. A wide range of applications uses this electrochemical option of energy storage as a strategic imperative. That includes powering up units in the military sector,  storing and providing energy for personal use, keeping uninterruptible power supply systems operational for data centers and hospitals, storing energy from photovoltaic systems, and enabling the operation of battery electric vehicles and power tools.

The rechargeable battery pack is the most common design in the accumulator segment and accounts for the major share of battery-powered applications. Such a pack usually consists of multiple Li-ion cells. With continuous technological development, the economics of the Li-ion rechargeable battery pack is also becoming attractive enough to warrant a substantial increase in its use. This is also leading to the miniaturization of individual cells, resulting in an increase in their energy density.

However, even with the increased availability and use, the Li-ion rechargeable battery pack continues to carry a residual risk of hazards, especially due to the increase in energy density brought on by miniaturization. The disadvantage is in terms of safety.

The electrolyte in the Li-ion cells is typically a mixture of organic solvents and a conductive salt that improves its electrical conductivity. Unfortunately, this also makes the mixture highly flammable. During operation, the presence of an inordinate thermal load can lead to the point where the mixture becomes explosive. Furthermore, this safety hazard to the end-user is increasing with the constant efforts to further increase the energy density of Li-ion cells.

Most electric battery cells have a narrow operational temperature range, varying from +15 °C to +45 °C. That makes temperature the key parameter. When the cell exceeds this temperature range, its rising heat becomes a threat to its functional safety, and to the safety of the overall system.

Overcharging the battery substantially increases the statistical probability of the defect in the cell. This may lead to a breakdown of the cell structure, typically associated with the generation of fire and in some cases, an explosion.

Manufacturers of rechargeable battery packs try to mitigate this risk by including a battery management system, and primary and secondary protection circuits that they embed in the electronic safety architecture of the battery. This allows the battery to remain within its specified operating range during the charging and discharging cycles. But nothing is immune to failure, including components in the protection circuit, and the battery system can ignite and explode on an excessively high load.

As the battery powers up a load, excessive current flow can heat up the battery, and the primary protection circuit may not detect it even when it exceeds the permissible level. For the protection of batteries, RUAG Ammotec is offering a heat lock element, a pyrotechnical switch-off device that is entirely independent of the battery system. This comprises a physicochemical sensor to continuously monitor the environmental heat. As the temperature rises, the sensor blocks the flow of current permanently. The heat lock element causes an insulating piston to shear off a current conductor, thereby electrically isolating the battery.

Battery Charge Controller Modules

Charge controllers prevent batteries from overcharging and over-discharging. Recharging batteries too often or discharging them excessively can harm them. By managing the battery voltage and current, a battery charge controller module can keep the battery safe for a long time.

Charge controllers protect the battery and allow it to deliver power while maintaining the efficiency of the charging system. Battery charge controller modules only work with DC loads connected to the battery. For AC loads, it is necessary to connect an inverter after the battery.

Charge controllers have a few key functions. They must protect the battery from overcharging, and they do this by controlling the charging voltage. They protect the battery from unwanted and deep discharges. As the battery voltage falls below a pre-programmed discharge value, the charge controller automatically disconnects the load. When the battery connects to a solar photovoltaic module, the charge controller prevents reverse current flow through the PV modules at night. The charge controller also provides information about the state of charge of the battery.

Various types of charge controllers are available in the market. Two of the most popular are the PWM or Pulse Width Modulation type and the MPPT or Maximum Power Point Tracking type. Although an MPPT type charge controller is more expensive than a PWM type, the former helps to boost the performance of solar arrays connected to the batteries. On the other hand, a PWM-type charge controller can extend the lifecycle of a battery bank at the expense of a lower performance from the solar panel. Typically, charge controllers exhibit a lifespan of about 15 years.

The XH-M60x family of battery charge controller modules is among the low-cost varieties offered by Chinese manufacturers. The most popular among them is the XH-M603. As the XH-M603 is not an overall charger, it is necessary to connect the battery to an external charger compatible to the battery.

The user can set optimal thresholds for initiating and terminating the battery charging cycle—making the charge controller a rather universal type, suitable for a wide range of batteries. Therefore, when the battery voltage falls below the set start value, the onboard relay starts routing the charging voltage from the charger to the battery. As soon as the battery voltage exceeds the stop value, the relay terminates the charging process.

XH-M603 battery charge controller module has a three-digit display on board for indicating the battery voltage. The display resolution is 0.1V. It accepts batteries with voltages between 12 and 24 V, Whereas it accepts input charging voltages between 10 and 30 VDC. The control precision is 0.1 V, while the DC voltage output tolerance is ±0.1 VDC. The overall dimensions of the module are 82 x 58 x 18 mm.

A small microcontroller controls the module, which has two voltage regulator chips onboard. There are a bunch of discrete components, including two micro-switches, a screw terminal block, an electromagnetic display, a three-digit Led display, and one red LED.

The charger connection to the module must maintain proper polarity. Likewise, the battery polarity is also important for the proper functioning of the module.

Rechargeable Batteries from Packing Materials

Sweden was in the news recently for their extreme recycling capacity. Swedes recycle waste to the extent that they have to import garbage from other countries for use as landfills. Others countries struggling to recycle their garbage may be interested in generating rechargeable batteries from discarded packing materials that do not degrade when used as landfills.

At Purdue University, researchers have found a new way to recycle discarded peanut-shaped packing materials. They are turning these materials into components that can be used for making rechargeable batteries. Additionally, they claim their batteries can outperform those currently in use.

Packing materials have always presented a challenge when they have to be disposed. It is not very cost-effective to recycle them. For one, they are light and their large size makes it expensive to transport them to the recycling center. Additionally, they take up a lot of space in landfills. Vinodkumar Etacheri, Ph.D. explained this in a presentation of the research at the National Meeting & Exposition of the American Chemical Society.

The other reason why packing materials are not suitable is they can be harmful to the environment. Although they may not contain CFCs or ozone depleting gasses, packing materials are usually made from recycled or new polystyrene, which was also used for making Styrofoam. While the exact constituents may vary, packing materials usually contain different types of chemicals.

Among them may be potentially harmful substances such as heavy metals, chlorides and phthalates. These leach into the environment easily when in a landfill. They deteriorate the soil and water quality. Although marketers claim newer material they use for making packing material is more environmentally friendly, the chemicals and detergents used in the starch-based alternatives also contaminate the ecosystem.

A new process developed by the researchers converts the packing material into high-tech nano-particles and carbon micro sheets. These are useful in making anodes for rechargeable batteries.

Lithium ion batteries have lithium ions moving between electrodes as the batteries charge and discharge. When the new anodes replace the conventional graphite ones in commercial lithium ion batteries, the performance gain is dramatic. The anodes made of nano-partcles and carbon micro sheets increase the storage capacity of the lithium ion batteries several folds.

The porous microstructure of the new anodes allows the lithium ions to diffuse in quickly and create more surface area within the micro sheets. The increased surface area offers greater electrochemical interactions. In addition, the disordered crystal structure and the porous nature of the new anodes can store more lithium ions beyond their theoretical limit.

According to the researchers, they use a relatively low temperature for the new process. This is a crucial factor in producing these new materials with their advantageous architecture. While other researchers make micro sheets at temperatures as high as 4,000°F, researchers at Purdue University have kept the temperature of their process at only 1,100°F. Instead of the more layered arrangement of carbon atoms at the higher temperature, the lower temperature generates less-ordered materials. That actually increases the electrical storage capacity by about 15%. The lower temperature process also allows the materials to remain more environmentally friendly.