What are the indicators of lithium-ion batteries that need to be paid attention?

The lithium-ion battery has a high energy density, high conversion efficiency, long cycle life, no memory effect, no charge, no discharge time delay, low self-discharge rate, wide temperature range and environment-friendly advantages, thus it becomes an ideal carrier of electric power and has been widely used in various fields.

In general, we in the use of the lithium-ion battery, it will focus on some technical indicators, as the main factor to measure its performance "and". What are we need at the time of use, should give special attention to?

The capacity of 1.

This is one of the biggest concerns of all parameters. Smartphones have already spread, we in the use of smartphones, the most worried about is the battery is low, need frequent charging, sometimes can't find the local charge. Early the function of the machine, under normal use, filled the battery could be standby 3 ~ 5 days, some products can even standby more than 7 days. But in the smartphone era, standby time is horrible. It's very important for one reason, is the power consumption is more and bigger, the mobile phone and battery capacity is not the same proportion of growth.

The capacity of the unit is common "mAh" (mAh) or "Ah" (Ann) when used with rated capacity and the difference between the actual capacity. Nominal capacity refers to the lithium-ion battery filled under laboratory conditions (temperature and humidity environment of ideal), with a certain discharge ratio (C - rate) discharge to the cut-off voltage, are able to provide the total power. Actual capacity is generally is not equal to the rated capacity, it is directly related to temperature, humidity, charge and discharge rate, etc. Under normal circumstances, the actual capacity is smaller than the rated capacity, sometimes even much smaller than the rating capacity, the winter in the north, for example, if in outdoor use of cell phones, battery capacity drops rapidly.

2. The energy density

Energy density, refers to the unit volume or weight of the battery, can store and release electricity, the unit has two kinds: Wh/kg and Wh/L, respectively than energy and volume weight. The power here is the above-mentioned capacity (Ah), and the integral working voltage (V). At the time of application, the energy density of this index given more has guiding significance.

Based on the current lithium-ion battery technology, can achieve the level of energy density about 100 ~ 200 Wh/kg, and the value is low, have had many occasions to become the bottleneck of lithium-ion battery applications. The problem also appeared in the field of electric vehicles, the volume and weight are tightly restricted conditions, determine the electric car battery energy density of single maximum mileage, then appeared the characteristic of the term "range anxiety". If you want to make electric cars single mileage reached 500 kilometers, and the traditional fuel car quite), the energy density of battery monomer must reach more than 300 Wh/kg.

Lithium-ion battery energy density of ascension, it is a slow process, of Moore's law is far lower than the integrated circuit industry, this can make the performance of electronic products with battery energy density between ascension scissors, and increasing with time.

3. The charge and discharge rate

This index will affect the lithium-ion battery work when continuous current and peak current, its unit is commonly C (C - the rate of abbreviations), such as C, 1/10 1/5 C, 1 C and 5 C, 10 C, etc. As an example to elaborate the specific meaning of ratio index, a capacity of the battery is 10 ah, if the nominal charge and discharge ratio is 1 c, that means this type of battery, can with 10 a current, repeated charge and discharge, until the cut-off voltage of charging or discharging. If the maximum discharge ratio is 10 c @ 10 s, maximum charging ratio 5 c @ 10 s, then the battery can be in the current of 100 a discharge for 10 seconds, for a 50 current charging for 10 seconds.

Charge and discharge rate corresponding to the current value multiplied by the working voltage can be concluded that the lithium-ion battery for power and peak power indicator. Charge and discharge ratio index defined more detailed when used for guiding significance. Especially as a lithium-ion battery of electric vehicle power supply, need rules under different temperature conditions of continuous and pulse rate index, to ensure that the lithium-ion battery used in a reasonable range.

4. The voltage

Lithium-ion battery voltage, there is open circuit voltage and working voltage, charging by some parameters such as voltage, discharge cut-off voltage, this paper no longer separate one by one, but make an explanation.

Open circuit voltage, just as its name implies, is the battery outside don't pick up any load or power, measuring the potential difference between a battery is negative, this is the open circuit voltage of the battery.

Working voltage, the external load is the battery or power, in working status, when we have current flow through measuring the potential difference between is negative. In general, as a result of the existence of battery internal resistance, working voltage is lower than the open circuit voltage of discharge state, the working voltage of charging is higher than the open circuit voltage.

Charge/discharge cut-off voltage refers to the highest and lowest battery allows achieving working voltage. Exceeded the limit, can produce some irreversible damage to the battery, resulting in a loss of battery performance, serious when even fire, explosion and other accidents.

Open circuit voltage and a working voltage of the battery, there is a certain corresponding relationship with the capacity of the battery.

Life of 5.

Lithium-ion battery life will gradually decay with use and storage, and there will be more obvious. Still in smart phones, for example, used mobile phones for a period of time, can clearly feel the phone battery "durable", may be charged only once a day, beginning may need to charge twice a day later, and this is the embodiment of the battery life constantly attenuation.

The life of the lithium-ion battery is divided into cycle life and the two parameters of the calendar life. For the unit with the number of cycle life in general, represent the number of batteries can be circulation charge and discharge. Here is conditional, of course, are usually under the ideal temperature and humidity, rated in the depth of the charge and discharge current charge and discharge (100% DOD or 80% DOD), calculation of battery capacity attenuation to 80% of the rated capacity, the cycles.

Calendar life is more complicated, the definition of a battery can't have been in charge and discharge, storage and shelving, could not have been ideal environmental conditions, will experience a variety of temperature and humidity conditions, charging and discharging rate is also a moment in change, so the service life of the actual need for simulation and testing. In simple terms, is the battery of the calendar life under the condition of using the environment, through the use of specific conditions, reach life termination conditions (such as capacity attenuation to 80%) the span of time. Calendar life and is closely combined with the use of specific requirements, usually need to prescribe specific operating conditions, environmental conditions, storage space, etc.

Then the cycle life of the calendar life more meaningful, but as a result of the calendar, life calculation is very complicated and time-consuming too long, so general battery manufacturer only cycles life of the data is given. As the calendar life they want to acquire data, usually to pay extra, and wait for a long time.

6. Internal resistance

Lithium-ion battery internal resistance is referred to the battery on the job, current flows through the battery internal resistance, which includes the ohmic resistance and the polarization resistance, polarization resistance and includes the electrochemical polarization resistance and the concentration polarization resistance.

Ohm internal resistance by the electrode material, electrolyte, the diaphragm of resistance and contact resistance of each part. Polarization resistance refers to the electrochemical reaction caused by the polarization resistance, including electrochemical polarization and concentration polarization resistance.

The unit of resistance is generally milliohm Ω (m), the internal resistance of the battery, at the time of charging and discharging, high internal power, serious fever, cause attenuation, accelerated aging and life of the lithium-ion battery can also limit the big ratio of charge and discharge applications. So, the smaller the resistance do, lithium-ion battery life and performance ratio will be the better.

7. Self-discharge

Battery at the time of place, its capacity is falling, the capacity decline rate is called the self-discharge rate, usually expressed as a percentage of % / month.

Self-discharge is we don't want to see, a fully charged battery, put a few months, the battery will be a lot less, so we hope the lithium-ion battery self-discharge rate is lower, the better.

Need special attention here, once the lithium-ion battery self-discharge of battery discharge, the impact is often irreversible, even if the recharging, available capacity of the battery will have a lot of damage, life will quickly decay. So is not in use for a long term of the lithium-ion battery, be sure to remember to recharge regularly, avoid because of self-discharge lead to discharge, performance affected by a lot.

8. Operating temperature range

Lithium-ion batteries due to the internal characteristics of chemical materials, lithium ion batteries have a reasonable working temperature range (common data between - 40 ℃ ~ 60 ℃), if beyond the scope of reasonable use, can cause great influence on the performance of lithium ion battery.

Different material of lithium-ion battery, its working temperature scope is also different, some have good high-temperature performance, some are able to adapt to low-temperature conditions. Lithium-ion batteries work parameters such as voltage, capacity, charge and discharge rate will be changed with the temperature, change is very significant. Using high and low temperatures for a long period of time also can accelerate the attenuation of lithium-ion battery life. Therefore, efforts to create a suitable operating temperature range, can the maximum limit of improving the performance of lithium-ion batteries.

In addition to the operating temperature limit, the lithium-ion battery also has strict constraints of storage temperature, high temperature or low-temperature storage for a long time, will cause irreversible influence to the battery performance.

The page contains the contents of the machine translation.