With the increasing applications of lithium-ion batteries in drones, electric vehicles (EV), and solar energy storage, battery manufacturers are using modern technology and chemical composition to push the limits of battery testing and manufacturing capabilities.

Nowadays, every battery, regardless of its size, performance, and life, is determined in the manufacturing process, and the testing equipment is designed around specific batteries. However, since the lithium-ion battery market covers all shapes and capacities, it is difficult to create a single, integrated testing machine that can handle different capacities, currents, and physical shapes with required accuracy and precision.

As the demand for lithium-ion batteries becomes more diversified, we urgently need high-performing and flexible testing solutions to maximize the pros and cons and achieve cost-effectiveness.

The complexity of a lithium-ion battery

Today, lithium-ion batteries come in a variety of sizes, voltages, and applications that were originally not available when the technology was first put on the market. Lithium-ion batteries were originally designed for relatively small devices, such as notebook computers, cell phones, and other portable electronic devices.

Now, they’re a lot bigger in size for such devices as electric cars and solar battery storage. This means that a larger series, the parallel battery pack has a higher voltage, larger capacity, and larger physical volume. Some electric vehicles can have up to 100 pieces of cells in series and more than 50 in parallel.

A typical rechargeable lithium battery pack in an ordinary notebook computer consists of multiple batteries in series. However, due to the larger size of the battery pack, the testing becomes more complicated, which may affect the overall performance.

In order to achieve the best performance of the entire battery pack, each battery must be almost the same as its adjacent cells. Batteries will affect each other: if one of the batteries in a series has a low capacity, the other batteries in the battery pack will be below the optimal state. Their capacity will be degraded by the battery monitoring and rebalancing system to match the battery with the lowest performance.

The charge-discharge cycle further illustrates how a single battery can degrade the performance of the entire battery pack. The battery with the lowest capacity in the battery pack will reduce its charging state at the fastest speed, resulting in an unsafe voltage level and causing the entire battery pack to be unable to discharge again.

When a battery pack is charged, the battery with the lowest capacity will be fully charged first, and the remaining batteries will not be charged further. In electric vehicles, this will result in a reduction in the effective overall available capacity, thereby reducing the vehicle’s range. In addition, the degradation of a low-capacity battery is accelerated because it reaches an excessively high voltage at the end of its charge and discharge before the safety measures take effect.

No matter the device, the more batteries in a battery pack that is stacked in series and in parallel, the more serious the problem.

The obvious solution is to ensure that each battery is manufactured exactly the same and to keep the same batteries in the same battery pack. However, due to the inherent manufacturing process of battery impedance and capacity, testing has become critical–not only to exclude defective parts but also to distinguish which batteries are the same and which battery packs to put in.

In addition, the charging and discharging curve of the battery in the manufacturing process has a great impact on its characteristics and is constantly changing.

Modern lithium-ion batteries bring new testing challenges

Battery testing is not a new thing, but, since its advent, lithium-ion batteries have brought new pressure to the accuracy of testing equipment, production capacity, and circuit board density.

Lithium-ion batteries are unique because of their extremely dense energy storage capacity, which may cause fires and explosions if they are improperly charged and discharged. In the manufacturing and testing process, this kind of energy storage technology requires very high accuracy, which is further aggravated by many new applications. The wide range of lithium-ion batteries that are available affects the testing equipment as they need to ensure that the correct charge and discharge curve is followed accurately in order to achieve the maximum storage capacity and reliability and quality.

Since there is no one size suitable for all batteries, choosing suitable test equipment and different manufacturers for different lithium-ion batteries will increase the test cost.

In addition, continuous industrial innovations mean that the constantly changing charge-discharge curve is further optimized, making the battery tester an important development tool for new battery technology. Regardless of the chemical and mechanical properties of lithium-ion batteries, there are countless charging and discharging methods in their manufacturing process, which pushes battery manufacturers to expect more unique test functions out of battery testers.

Accuracy is obviously a necessary capability. It not only refers to the ability to keep high current control accuracy at a very low level but also includes the ability to switch very quickly between charging and discharging modes and between different current levels. These requirements are not only driven by the need to mass-produce lithium-ion batteries with consistent characteristics and quality but also by the hope to use testing procedures and equipment as innovative tools to create a competitive advantage in the market.

Although a variety of tests are required for different types of batteries, today’s testers are optimized for specific battery sizes. For example, if you are testing a large battery, a larger current is required, which translates to larger inductance, thicker wires, etc. So many aspects are involved when creating a tester that can handle high currents.

However, many factories do not only produce one type of battery. They may produce a complete set of large batteries for a customer while meeting all the test requirements for these batteries, or they may produce a set of smaller batteries with a smaller current for a smartphone customer.

This is the reason for the rising cost of testing–the battery tester is optimized for the current. Testers that can handle higher currents are generally larger and more expensive because they not only require larger silicon wafers but also magnetic components and wiring to meet electromigration rules and minimize voltage drops in the system. The factory needs to prepare a variety of testing equipment at any time to meet the production and inspection of various types of batteries. Due to the different types of batteries produced by the factory at different times, some testers may be incompatible with specific batteries and may be left unused.

Whether it is for today’s emerging factories for mass production of ordinary lithium-ion batteries or for battery manufacturers who want to use the testing process to create novel battery products, flexible test equipment must be used to adapt to a wider range of batteries’ capacity and physical size, thereby reducing capital investment and improving the return on investment.

Lithium iron phosphate(LiFePo4) batteries are continually sought after in the battery market for their long life and safety. This is seen recently with Tesla’s Model 3 and BYD’s Han series launching with LiFePO4 batteries.

We will explore these pros and cons of LiFeP04 batteries in this article.

You may have heard that there are restrictions when flying your drone in high temperatures, but did you know that it’s a similar case in low temperatures too?

We will explore some factors to consider if you plan on flying your drone in cold weather.

The impact of low temperatures on drones

Lower temperatures slow down the chemical reaction of LiPo (lithium-ion polymer) batteries, thereby reducing battery capacity, increasing resistance, and shortening the flight time. Drone manufacturer DJI states on its website that the LiPo batteries that power their drones start draining at an increased rate at temperatures below 59℉ (15°C).

It’s important that users read the manuals for their drones before a flight.  The operator temperature of most drones is set at 32 to 104 ℉ (0 to 40°C), so you should avoid flying outside of this temperature range.

To fly a drone in low-temperature, you need to prepare in all aspects.

Measure

Before going out

Plan your day out beforehand and try to finish your flight as soon as possible before it gets too dark. See the weather forecast: if there’s snow, hail, or rain, reschedule your flight as these weather conditions can damage your equipment and drones and very likely cause a crash.

Ensure your batteries are fully charged and have spare ones on hand to switch out.

When going out

Limit direct exposure of your batteries to the cold air. Keep them in their gear or protective equipment instead of just in the trunk of your vehicle.

Take off

When launching your drone, raise the aircraft 10-20 feet from the ground and make it hover for 30-60 seconds. This can increase the temperature of the battery to achieve a warm-up effect. Some apps, such as the DJI GO, allow you to check and monitor the battery temperature.

Focus on the battery’s voltage. You should keep the battery’s voltage indicator displayed on your monitor so you can keep track of it.

Check the components. In a cold environment, some parts, like propellers, become more fragile. Therefore, it is necessary to check them more diligently for cracks or damage. You can also consider replacing them with solid carbon fiber blades.

Avoid running out of capacity. Fly until the battery drops to 30-40% of its capacity, and then bring the drone back down. In order to prevent other unpredictable situations from happening, don’t drain your battery completely when flying.

Stop flying immediately if it starts to rain or snow.  Be careful because most drones are not waterproof. Moisture may short-circuit the motor and cause the drone or controller to malfunction.

For you

Don’t forget to keep yourself warm. It is best to wear gloves which can touch the screen because it will be very inconvenient to operate the device with cold and stiff hands.

Wear goggles. When flying in icy or snow-covered weather, your eyes may be damaged due to the greater light reflection. Goggles can avoid this problem.

 

 

 

The voltage of a lithium-ion battery is determined by the electrode potential. Voltage, also known as potential difference or potential difference, is a physical quantity that measures the energy difference of electric charges in an electrostatic field due to different potentials. The electrode potential of lithium-ion batteries is about 3V, and the voltage of lithium-ion batteries varies with different materials. For example, a general lithium-ion battery has a nominal voltage of 3.7V and a full-charge voltage of 4.2V; a lithium iron phosphate battery has a nominal voltage of 3.2V and a full-charge voltage of 3.65V. In other words, the potential difference between the positive electrode and the negative electrode of a lithium-ion battery in practical use cannot exceed 4.2V, which is a requirement based on material and use safety.

If the Li/Li+ electrode is used as the reference potential, μA is the relative electrochemical potential of the negative electrode material, μC is the relative electrochemical potential of the positive electrode material, and Eg, the electrolyte potential range, is the difference between the lowest electron unoccupied energy level and the highest electron occupied energy level. So the maximum voltage of the lithium-ion battery is determined by μA、μC、Eg.

The difference between μA and μC is the open-circuit voltage (the highest voltage value) of the lithium-ion battery. When this voltage value is in the Eg range, the normal operation of an electrolyte can be ensured. Normal operation means that the lithium-ion battery moves back and forth between the positive and negative electrodes through the electrolyte, but does not undergo oxidation-reduction reactions with the electrolyte, So as to ensure the stability of the battery structure. The electrochemical potential of the positive and negative materials causes the electrolyte to work abnormally in two forms:

1. When the electrochemical potential of the negative electrode is higher than the lowest electron and unoccupied energy level of the electrolyte, the electrons of the negative electrode will be captured by the electrolyte, and the electrolyte will be oxidized, then the reaction product will form a solid-liquid interface layer on the surface of the negative electrode material particles. As a result, the negative electrode may be damaged.
2. When the electrochemical potential of the positive electrode is lower than the highest electron-occupied energy level of the electrolyte, the electrons in the electrolyte will be captured by the positive electrode and oxidized by the electrolyte. Then the reaction product forms a solid-liquid interface layer on the surface of the positive electrode material particles, resulting in the positive electrode may be damaged.

However, the possibility of damage to the positive or negative electrode is due to the existence of the solid-liquid interface layer, which prevents the further movement of electrons between the electrolyte and the positive and negative electrodes, and instead protects the electrode material. That is to say, the lighter solid The liquid interface layer is protective. The premise of this protection is that the electrochemical potential of the positive and negative electrodes can slightly exceed the Eg interval, but not too much. For example, the reason why most of the current lithium-ion battery anode materials use graphite is that the electrochemical potential of graphite related to Li/Li+ electrodes is about 0.2V, which slightly exceeds the Eg range (1V~4.5V), but because of its protective properties, the solid-liquid interface layer prevents the electrolyte from being further reduced, thus stopping the continuous development of the polarization reaction. However, the 5V high-voltage cathode material is far beyond the Eg range of the current commercial organic electrolyte, so it is easily oxidized during charging and discharging. With the increase of charging and discharging times, the capacity decreases and the service life also decreases.

The reason why the open-circuit voltage of the lithium-ion battery is selected to be 4.2V is that the Eg range of the electrolyte of the existing commercial lithium-ion battery is 1V ~ 4.5V. If the open-circuit voltage is set to 4.5V, the output power of the lithium-ion battery may be increased, but it also increases the risk of battery overcharge, and the harm of overcharge has been explained by a lot of data, so there is no additional explanation here.

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