Safety considerations in lithium-ion battery design

Using the wrong battery under the wrong conditions can cause problems and explosions. Careful design can avoid accidents such as battery rupture and explosion, and reduce the risk of harmful electrochemical reactions and mistakes.

Lithium ion batteries have many advantages over other rechargeable batteries, including high energy density, light weight, long life cycle, good capacity maintenance characteristics, large environmental temperature range and current endurance, and so on. Lithium-ion batteries are more adaptable to the environment than other chemical batteries, but their large capacity means they must be designed to be more secure.

Safety design can avoid many accidents

Use situation

An important step in choosing a lithium-ion battery pack is to give a "true picture" of the device. For example, the temperature limits of different devices can cause the same battery to behave differently. The battery usage profile includes the following parameters, such as operating voltage range, current duty ratio, environment and operating temperature, periodic behavior, charging and operating time, frequency, and number of charging and discharging cycles. Battery manufacturers' specifications do not contain such details during the design and development process. Only when all the parameters are known can the battery pack be seamlessly integrated into a portable device.

The best battery design should include a redundant protection circuit so that the auxiliary circuit can function even if the main circuit fails. In this way, the battery will fail only in one case, that is, all the circuits will fail at the same time.

Components of a battery pack

In addition to multiple protection circuits and thermal sensors, the smart battery pack also has advanced intelligent functions. The battery pack typically includes a communications component that measures the number of charges and discharges, as well as a fuel meter to track the rest of each cycle and report on the battery's safety.

Voltage-based fuel meters rely heavily on periodic voltage measurements to understand battery capacity. This approach has its limitations, as it can only estimate relative capacity and give overshoot information. The linear method calculates the battery capacity by measuring the total input current. This method requires the cooperation of the microprocessor to monitor the voltage drop through the induction resistance connected between the negative terminal of the battery and the ground, so as to determine the charging and discharging activities of the battery. Two - wire or coulomb metering can be used to evaluate the absolute capacity of the battery. The most common protocols in the two-wire approach are I2C and SMBus.

Once the battery pack is assembled, most fuel meters complete a "learning loop" so that the battery can remember which parts are empty and which are full, and then set up the fuel meter correctly. But the most advanced fuel gauges, which can achieve 99 percent accuracy even without a learning period, are often used in critical applications.

Smart battery systems are an important choice for many advanced handheld devices. Their advanced features allow end users to intelligently manage devices and avoid failures or shutdowns.

Figure 2 charging state controlled by microprocessor

Protective measurement

Safety measurements inside a lithium battery depend on a thermal shut-off isolator, which separates anode and cathode material and USES a material to ensure that the internal resistance increases when the battery temperature exceeds the shut-off point.

In addition, the battery certification process is very useful. When a battery with a tiny controller communicates with the processor embedded in the main device, the battery pack starts the authentication process. This certification not only protects against malfunctions caused by improper use of battery packs, but also prevents the use of reverse system programs to steal battery patents.

The materials used in batteries are also monitored because the heavy metals in the battery pack must be limited. The European RoHS directive does not currently apply to batteries, and some equipment is currently managed through the European battery directive 91/157/EEC, which includes the requirement to recycle batteries.

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