E-bike Battery

Lithium batteries for electric bicycles can be roughly divided into three categories: lithium manganate batteries, Li(NiCoMn)O2 batteries and lithium iron phosphate batteries.

Lithium manganate battery: In order to solve the high temperature performance of lithium manganate battery, the cathode material, battery structure design and electrolyte formula must be improved. Modified lithium manganate batteries were used in Japan and Korea. The capacity of modified lithium manganate batteries was just reduced to 99% when they were stored at 65 C for one week.

Li(NiCoMn)O2 material batteries: lithium batteries with cobalt, nickel and manganese as cathode materials overcome the shortcomings of poor high temperature performance of lithium manganate and increase the specific energy of batteries.

Lithium iron phosphate battery: Since 2002, the United States and Canada began to develop lithium iron phosphate battery, which has become a new power lithium battery with great development prospects. Super long life, at room temperature 1C charge and discharge cycle up to 2000 times.

Advantages of lithium iron phosphate batteries: high safety. Phosphate chemical bond has strong binding force and good structural stability; environmental protection and does not contain any heavy metals; non-toxic (SGS certified), non-polluting; fast charging speed,  lithium iron phosphate battery can fast charge and discharge at high current 5-10C; high current discharge performance is good; 10-50C high current and high power discharge.

The disadvantage of lithium iron phosphate battery is that its low temperature performance is inferior to other cathode materials such as lithium manganate. The monomer voltage of lithium iron phosphate battery is 3.2V. A 36V battery pack requires 12 individual batteries in series. At present, the life of single lithium iron phosphate battery is over 2000 times, but the life of battery pack may only be 500 times.

Advantages and disadvantages of lithium batteries for electric bicycles

(1) Advantages of lithium batteries for electric bicycles

The energy of lithium batteries is twice more than the lead-acid batteries. At present, the electric bicycles charged with lead-acid batteries can drive 50-70 km at a time, and the lithium batteries with the same weight can drive 100-150 km at a time. The times of charges and discharges of lithium batteries is also high. The problem is that the price is 6 times higher than lead-acid batteries, and it needs 1800-2000RMB for each vehicle. Moreover, the existing specifications are all small size for mobile phones and notebook computers, and larger size over 10Ah needs to be developed. At present, this kind of battery can only be used for luxury bicycles or electric motorcycles, but it has great potential for price reduction and has good prospects.

Lithium battery electric bicycle has the advantages of long life, light weight and small size. There is a compact lithium battery electric bicycle, which weighs only about 16 kilograms. The battery is only the size of a book and weighs only 2.5 kilograms. It can be carried in a bag and used to charge a computer. The lead-acid battery weighs about 15 kilograms. However, the price of this kind of electric car is relatively expensive, which requires more than 2,800RMB . "This kind of car has only been on the market for a week, and its price is relatively high, but its sales are better than expected. Several cars are sold in a week." Mr. Zhang, the head of the Green Energy Electric Vehicle, introduced that this kind of vehicle uses lithium batteries and can run about 30 kilometers once charged. There are also lithium battery electric cars in brand stores such as Giant and Bridgestone. "The power performance of lithium battery electric bicycle is similar to that of lead-acid battery, charging for 6-8 hours, running 30-45 kilometers depending on the battery capacity, and weighing only about one fifth of the lead-acid battery." According to Giant's sales staff, the biggest advantage of lithium-ion battery electric bicycles is their long life. A battery pack can be used for 4 to 5 years, while lead-acid batteries only have a life of about 2 years.

(2) Disadvantages of lithium batteries for electric bicycles

The disadvantage of lithium batteries is that the price is too high and the market share is only 4%. At present, the price of lithium battery electric bicycle is generally several hundred to one thousand RMB higher than that of lead-acid battery electric bicycle, so the sales volume is not large. "The difference between the two is more than 800 RMB. If it's only two or three hundred RMB, I might consider it." Ms. Zhang, who is buying an electric bicycle, finally bought a traditional lead-acid battery electric bicycle.

Problems and Solutions of Lithium Batteries for Electric Bicycles

Lithium batteries have not been used in electric bicycles for a long time, and their technology has not reached a high level. Therefore, there are still many technical problems, which restrict the development of lithium batteries industry of electric bicycles to a certain extent.

At present, the main problem of lithium-ion batteries for electric bicycles is the safety problem in the use process. How to solve the safety problem has become a trend of the development of lithium-ion batteries for electric bicycles in the future. Here we briefly introduce how to solve this problem.

(1) Overcharging

Normal lithium should be charged up to 4.2 volts. On this basis, iron-lithium batteries should be reduced by 0.5 volts as the upper and lower limits, and charged above 4.3 volts as overcharge. To solve this problem, we need to accurately measure the true value of voltage: using scientific charging method, full but not over-charged; reasonable setting of single overcharge protection voltage point: such as: 4.2V (+0.05V), to ensure that no overcharge and explosion.
(2) Overdischarge

The discharge of lithium batteries is 3.2 volts at the lowest, and the discharge below 3 volts is over-discharge. Accurate measurement of the true value of electric power: scientific and safe discharge mode is adopted to discharge without over-discharge; reasonable setting of single section over-discharge protection voltage point: For example ,3.20V+0.05V to ensure that no over-discharge and explosion occurs.

(3) Battery temperature detection

High temperature of lithium batteries may cause explosion. Therefore, it is necessary to monitor the temperature of each battery to ensure that it does not explode because of the high temperature of the battery.

(4) Overcurrent protection

Lithium batteries have a rated current, which is not allowed to exceed the rated current, otherwise the battery will burn out. Therefore, it is necessary to accurately measure and control the charging and discharging current, and take over-current protection measures efficiently and quickly. When the current exceeds the setting current, short circuit and reverse connection accidents should be avoided.

(5) Equilibrium

There are deviations in the monomer voltage of lithium ion batteries. Without balanced control, with the increase of charging and discharging cycles, the monomer batteries will gradually differentiate and their service life will be greatly reduced. When charging and discharging a lithium-ion battery pack, considering the inconsistency of individual batteries, balancing measures can be taken to ensure safety and stability.

Lithium batteries are widely used in energy storage power supply systems, uninterrupted power supply for post and telecommunications, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

Although the application of lithium batteries in the field of electric bicycles has not reached a mature level, the current good development prospects and the excellent characteristics of lithium batteries in the field of electric bicycles have made the development of lithium-based electric bicycles more rapid.

In addition, large capacity lithium-ion batteries have been tested in electric vehicles, and are expected to become one of the main power sources of electric vehicles in the 21st century, and will be used in artificial satellites, aerospace and energy storage.

With the shortage of energy and the pressure of environmental protection in the world. Lithium power is now widely used in electric vehicle industry, especially the emergence of lithium iron phosphate batteries, which promotes the technological progress and breakthrough of lithium battery industry.

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