Characteristics and applications of portable power lithium batteries

1 Features

1.1 Single cell operating voltage up to 3.7V

It is three times that of nickel-cadmium batteries and nickel-metal hydride batteries, and nearly twice that of lead-acid batteries. This is also an important reason why lithium-ion power batteries have high specific energy. Therefore, when forming a power battery pack of the same voltage, the number of lithium-ion power batteries used in series will be much less than that of lead-acid batteries and nickel-metal hydride batteries. The more single cells there are in the power battery, the higher the consistency requirements of the single cells in the battery pack, and the more difficult it is to make the life span. After analyzing the problems of the battery pack in actual use, it is generally one or two of the single cells that have problems and then cause problems in the entire battery pack. Therefore, it is not difficult to understand why the feedback of 48V lead-acid batteries is higher than that of 36V lead-acid batteries. From this perspective, lithium batteries are more suitable for the use of power batteries. For example, a 36V lithium battery only needs 10 single cells, while a 36V lead-acid battery needs 18 single cells, that is, 3 12V battery packs, and each 12V lead-acid battery has six cells, that is, six single cells.

1.2 Small size and light weight

The specific energy is large, up to 150Wh/Kg, which is twice that of nickel-metal hydride batteries and four times that of lead-acid batteries. Therefore, the weight is one-third to one-quarter of the lead-acid battery with the same energy. From this perspective, lithium batteries consume less resources, and because the reserves of elements used in lithium manganese oxide batteries are relatively large, the price may rise further relative to lead-acid and nickel-metal hydride batteries, and the cost of lithium-ion power batteries is further reduced. The weight of lithium batteries for electric bicycles is 2.2-4 kg, and the weight of lead-acid batteries is 12-20 kg. The weight of lithium batteries is about one-quarter to one-third of that of lead-acid batteries, which is about 10 kg lighter than lead-acid batteries (36V, 10Ah batteries). The weight of the battery is reduced by 70%, and the total weight of the vehicle is reduced by at least 20%. In addition, general lithium-ion electric vehicles are simple electric bicycles. Because the battery and the whole vehicle are light, the battery with the same voltage and capacity has a longer driving range. Ordinary electric vehicles weigh more than 40 kg, while lithium-ion power battery electric bicycles weigh between 7 and 26 kg. Ladies and the elderly can move it easily, and human-powered riding is also very convenient, allowing for both sports and leisure.

Small size, up to 400Wh/L, the volume is one-half to one-third of that of lead-acid batteries. It provides design conditions, design space and possibilities for a more reasonable structure and a more beautiful appearance. At present, due to the limitations of the volume and weight of lead-acid batteries, designers' design ideas are greatly constrained, resulting in the current electric bicycles being "one-size-fits-all", similar, and monotonous in structure and appearance. The use of lithium-ion batteries provides designers with greater space and conditions to display design ideas and styles. Of course, it also leads to a variety of sizes of lithium-ion power batteries for electric bicycles, which is not conducive to the development of the lithium power battery industry. The lithium power battery industry also needs to formulate national standards for electric vehicle batteries as soon as possible to accelerate the replacement of lithium batteries for lead-acid batteries in the field of electric bicycles. Of course, lithium batteries are currently in the process of continuous development, and the volumes of batteries with different materials and processes are very different, so how to unify them is also a difficult point.

1.3 Long cycle life

The number of cycles can reach 1000 times. Assuming the capacity is maintained at 60%, the battery pack can be cycled for more than 600 times at 100% charge and discharge, and the service life can reach 3-5 years, which is about two to three times that of lead-acid batteries. With the innovation of technology and the improvement of equipment, the battery life will be longer and longer, and the cost performance will be higher and higher. The self-discharge rate is low, less than 5% per month.

1.4 Wide operating temperature range

Good low-temperature performance. Lithium-ion power batteries can operate between -20℃ and +55℃, which is especially suitable for low-temperature use. However, aqueous solution batteries (such as lead-acid batteries and nickel-metal hydride batteries) will have greatly reduced performance at low temperatures due to the poor fluidity of the electrolyte.

1.5 No memory effect

Therefore, it does not need to be discharged before each charge like Ni-Cd batteries and Ni-MH batteries, and can be charged anytime and anywhere. The depth of battery charge and discharge has little effect on the battery life, and it can be fully charged and fully discharged. Our cycle test is fully charged and fully discharged.

1.6 Particularly suitable for power batteries

In addition to the high voltage of lithium-ion batteries, the protection board of the lithium-ion power battery pack can monitor each single battery with high precision.

Low power consumption intelligent management, with perfect overcharge, over discharge, temperature, over current, short circuit protection, lock self-recovery function and reliable balanced charging function, greatly prolongs the battery life. Other types of batteries (such as lead-acid batteries) are prone to battery overcharge, over discharge and other problems during use due to battery consistency, charger and other issues (due to cost and other reasons, lead-acid battery packs cannot monitor and protect every single cell).

1.7 No pollution

Lithium-ion power batteries do not contain toxic substances, so they are called "green batteries" and are given key support by the state. However, due to the presence of harmful substances such as lead and cadmium in lead-acid batteries and nickel-cadmium batteries, the state will inevitably strengthen supervision and governance (cancellation of export tax rebates for lead-acid batteries, increase in lead resource taxes, and restrictions on the export of lead-acid electric bicycles), and the costs of corresponding companies will also increase. Although lithium batteries do not pollute, from the perspective of resource conservation. The recycling of lithium-ion power batteries, the safety of recycling, and the cost of recycling also need to be considered.

2 Disadvantages

2.1 Security risks

Due to the high energy and poor material stability of lithium-ion power batteries, lithium batteries are prone to safety problems. Currently, the world's well-known mobile phone and laptop battery (positive electrode materials are lithium cobalt oxide and ternary materials) manufacturers, such as Japan's Sanyo and Sony, require the battery explosion rate to be controlled below 40 ppb (parts per billion). Domestic companies are already good enough to reach the ppm (parts per million) level. The capacity of power batteries is more than a hundred times that of mobile phone batteries, so the safety requirements for lithium batteries are extremely high. Although lithium cobalt oxide batteries and ternary material batteries have the advantages of lighter weight and smaller size, they are not suitable for use as power batteries in electric vehicles.

2.2 High price

The price of lithium-ion power batteries with the same voltage and capacity is 3-4 times that of lead-acid batteries. With the expansion of the lithium-ion power battery market, the reduction of costs, the improvement of performance, and the increase in the price of lead-acid batteries, the cost performance of lithium-ion power batteries is likely to exceed that of lead-acid batteries.

2.3 Structure

Lithium-ion power batteries usually have two appearances: cylindrical and rectangular. The battery interior adopts a spiral winding structure, and a very fine and highly permeable polyethylene or polypropylene or polyethylene and polypropylene composite film isolation material is used to separate the positive and negative electrodes. The positive electrode includes a lithium ion collector composed of a lithium-containing material (such as lithium cobalt oxide, lithium manganese oxide, one or a mixture of nickel cobalt manganese oxide, etc.) and a current collector composed of an aluminum film. The negative electrode is composed of a lithium ion collector composed of a layered carbon material and a current collector composed of a copper film. The battery is filled with an organic electrolyte solution. In addition, a safety valve and a PTC element are installed to protect the battery from damage when the battery is in an abnormal state and the output is short-circuited.

The voltage of a single lithium battery is 3.6V, and its capacity cannot be infinite. Therefore, single lithium batteries are often connected in series or parallel to meet the requirements of different occasions.

3 Applications

3.1 Application Group

With the development of microelectronics technology in the 20th century, the number of miniaturized devices has increased, which has put forward high requirements on power supply. As a result, lithium-ion power batteries have entered the large-scale practical stage.

Lithium-ion power batteries generally have a nominal voltage higher than 3.0 volts and are more suitable for use as integrated circuit power supplies. Manganese dioxide batteries are widely used in computers, calculators, cameras, and watches.

Nowadays, lithium-ion power batteries are widely used in mobile phones, which can be said to be the largest application group.

3.2 Examples

(1) There are many battery packs for battery pack repair and replacement, such as those used in laptop computers. After repair, it was found that when this battery pack is damaged, only individual batteries have problems. You can choose a suitable single-cell lithium battery for replacement.

(2) Making a high-brightness miniature flashlight I have used a single 3.6V1.6AH lithium battery and a white ultra-high brightness light-emitting tube to make a miniature flashlight that is easy to use, compact and beautiful. And because the battery capacity is large, it can be used for an average of half an hour every night, and it has been used for more than two months without charging.

(3) Replacement of 3V power supply. Since the voltage of a single lithium battery is 3.6V, only one lithium battery can replace two ordinary batteries to power small household appliances such as radios, walkmans, cameras, etc. It is not only light in weight but also has a long continuous use time.

3.3 Scientific research

In order to develop varieties with better performance, people have studied various materials. Thus, unprecedented products have been produced. For example, lithium sulfur dioxide batteries and lithium thionyl chloride batteries (i.e., lithium-thionyl chloride batteries) are very unique. Their positive electrode active materials are also the solvents of the electrolyte. This structure only appears in non-aqueous electrochemical systems. Therefore, the research on lithium batteries has also promoted the development of electrochemical theories of non-aqueous systems. In addition to using various non-aqueous solvents, people have also conducted research on polymer thin film batteries.

In the 21st century, scientists developed a new type of lithium iron phosphate power battery. The characteristics of lithium iron phosphate batteries can be summarized as follows:

A High efficiency output: standard discharge is 2~5C, continuous high current discharge can reach 10C, instantaneous pulse discharge (10S) can reach 20C;

B. Good performance at high temperature: when the external temperature is 65℃, the internal temperature is as high as 95℃. When the battery is discharged, the temperature can reach 160℃. The battery structure is safe and intact.

C Even if the battery is damaged internally or externally, the battery will not burn or explode, and is the safest;

D. Excellent cycle life, after 500 cycles, its discharge capacity is still greater than 95%;

E will not be damaged even if it is over-discharged to zero volts;

F can be charged quickly;

G Low cost;

H No pollution to the environment.

Because lithium iron phosphate power batteries have the above characteristics and various batteries with different capacities are produced, they are quickly widely used. Its main application areas are:

Large electric vehicles: buses, electric cars, tourist attractions buses and hybrid vehicles, etc.;

Light electric vehicles: electric bicycles, golf carts, small flat battery vehicles, forklifts, cleaning vehicles, electric wheelchairs, etc.;

Power tools: electric drill, electric saw, lawn mower, etc.;

Remote control cars, boats, airplanes and other toys;

Energy storage equipment for solar and wind power generation;

UPS and emergency lights, warning lights and mining lamps (the safest);

Replaces 3V disposable lithium batteries and 9V NiCd or NiMH rechargeable batteries in cameras (exactly the same size);

Small medical instruments and portable instruments, etc.

Lithium iron phosphate batteries will be the mainstream in the future power battery market.