Some common sense about lithium batteries

Portable electronic products use batteries as power sources. With the rapid development of portable products, the use of various batteries has greatly increased, and many new types of batteries have been developed. In addition to the more familiar high-performance alkaline batteries, rechargeable nickel-cadmium batteries, nickel-metal hydride batteries, there are lithium batteries developed in recent years. This article mainly introduces the basic knowledge about lithium batteries. This includes its characteristics, main parameters, the meaning of the model, the scope of application, and the precautions for its use.

Lithium is a metal element whose chemical symbol is Li (its English name is lithium). It is a silver-white, very soft, chemically active metal and is the lightest in metals. In addition to its application in the Atomic energy industry, it can produce special alloys, special glass (fluorescent glass for television machines) and lithium batteries. It is used as an anode for batteries in lithium batteries.

Lithium batteries are also divided into two categories: non-rechargeable and rechargeable. Non-rechargeable batteries are called disposable batteries. They can only convert chemical energy into electrical energy at once, and can not restore electrical energy back to chemical energy (or have poor reduction performance). The rechargeable battery is called a quadratic battery (also known as a battery). It can convert electrical energy into chemical energy and store it. When used, it converts chemical energy into electrical energy. It is reversible, such as the main feature of electric energy chemical energy lithium batteries.

Smart portable electronic products require small size and light weight, but the size and weight of the battery are often the largest and heaviest compared with other electronic components. For example, the "big brother" in the past was quite "thick and bulky", and today's mobile phones are so light. Among them, the improvement of batteries played an important role: in the past, nickel-cadmium batteries were now lithium-ion batteries.

The biggest feature of lithium batteries is that they are higher than energy. What's more than energy? Specific energy refers to the energy per unit weight or unit volume. The specific energy is expressed as Wh/kg or Wh/L. Wh is the unit of energy, W is tile, H is hour; Kg is kg(mass unit) and L is L(volume unit). Here is an example to illustrate: The rated voltage of the nickel-cadmium battery No. 5 is 1 2 V, and its capacity is 800 mAh, and its energy is 0 960 Wh(1 2 V × 0 8 Ah). The rated voltage of the same size lithium-manganese dioxide battery No. 5 is 3V, and its capacity is 1200 mAh, and its energy is 3.06 Wh. The volume of these two batteries is the same, then the specific energy of the lithium-manganese dioxide battery is 375 times that of the nickel-cadmium battery!

A section 5 nickel-cadmium battery weighs about 23g, while a section 5 lithium-manganese dioxide battery weighs about 18g. A lithium-manganese dioxide battery is 3V, while two nickel-cadmium batteries are only 24V. Therefore, when using lithium batteries, the number of batteries is small (reducing the volume and weight of portable electronic products), and the battery has a long working life.

In addition, lithium batteries have the advantages of stable discharge voltage, wide operating temperature range, low self-discharge rate, long storage life, no memory effect and no pollution.

The disadvantage of lithium batteries is that they are expensive, so they can not be widely used at present. They are mainly used in handheld computers, PDAs, communications equipment, cameras,specials,specials,speciales, and instruments. With the development of technology, the improvement of the process and the increase in production, the price of lithium batteries will continue to decline, and applications will also be more common.

Non-rechargeable lithium batteries

There are many types of non-rechargeable lithium batteries. Currently, lithium-manganese dioxide batteries, lithium-thionyl chloride batteries, and lithium and other compound batteries are commonly used. This article only introduces the first two most commonly used ones.

Lithium-manganese dioxide battery (Li-MnO2)

Lithium-manganese dioxide battery is a disposable battery with lithium as the anode, manganese dioxide as the cathode, and organic electrolytes. The main feature of the battery is its high battery voltage and rated voltage of 3V(2 times that of a general alkaline battery); The termination discharge voltage is 2V; More than energy(see example above); The discharge voltage is stable and reliable; Good storage performance(more than 3 years storage time), low self-discharge rate(annual self-discharge rate ≤ 2 <UNK>); Operating temperature range -20 °C ~ +60 °C.

The battery can be made into different shapes to meet different requirements. It has rectangular, cylindrical and button-shaped(button-type). Cylinders also have different diameters and height sizes. Here are the main parameters of the familiar 1 # (size code D), 2 # (size code C) and 5 # (size code AA) batteries.

CR is expressed as a cylindrical lithium-manganese dioxide battery; Of the five digits, the first two represent the diameter of the battery, and the last three represent the height with one decimal. For example, the CR14505 has a diameter of 14mm and a height of 50,05mm (this model is universal).

It is pointed out here that there may be some differences in the parameters of the same type of battery produced in different factories. In addition, the standard discharge current value is small, the actual discharge current can be greater than the standard discharge current, and the allowed discharge current of continuous discharge and pulse discharge is also different, and the relevant data is provided by the battery plant. For example, the CR14505 produced by Lixing Power Co., Ltd. gives a maximum continuous discharge current of 1000mA and a maximum pulse discharge current of 2500mA.

Lithium batteries used in cameras are mostly lithium-manganese dioxide batteries. Lithium-manganese dioxide batteries commonly used in cameras are listed here in table 2 for reference.

The button-type(button-type) battery is smaller in size, with a diameter of 12.05 to 24.05 mm and a height of 1.06 to 5.0 mm. Several of the more commonly used button batteries are shown in Table 3.

CR is a cylindrical lithium-manganese dioxide battery. The first two of the last four digits are the diameter dimensions of the battery, and the last two are the height sizes with decimal points. For example, the CR1220 has a diameter of 12.05 mm(excluding the number of decimal points) and its height is 2.0 mm. This model representation method is internationally used.

This type of button battery is often used for clocks, calculators, electronic notepads, cameras, hearing aids, electronic game consoles, IC cards, and backup power supplies.

Lithium-thionyl chloride battery (Li-SOCl2)

Lithium-thionyl chloride cells are the most energy-specific and currently reach 500 W/kg or 1000 Wh/L levels. Its rated voltage is 3.06 V, which has an extremely flat 3.04 V discharge characteristic when discharged with a medium current (it can be discharged flat within a 90-inch capacity range with little change). The battery can work within the range of -40 °C to +85 °C, but the capacity at -40 °C is about 50 <UNK> of room temperature capacity. The self-discharge rate is low (annual self-discharge rate ≤ 1 <UNK>) and the storage life is more than 10 years.

A comparison is made between the specific energy of a # 1(size code D) nickel-cadmium battery and a # 1 lithium-thionyl chloride battery: the rated voltage of a # 1 nickel-cadmium battery is 1,2V and the capacity is 5000mAh; 1 # Lithium-thionyl chloride has a rated voltage of 3.06 V and a capacity of 10,000 mAh, then the latter is 6 times larger than the former!

Application Note

The above two lithium batteries are disposable batteries and can not be charged(dangerous when charging! ); Do not short-circuit between the positive and negative poles of the battery; No discharge of excessive current(above the maximum discharge current discharge) shall be permitted; When the battery is used to terminate the discharge voltage, it should be removed from the electronic product in time; Do not crush, burn or disassemble used batteries; Not to be used beyond the specified temperature range.

Since the voltage of lithium batteries is higher than that of ordinary batteries or nickel-cadmium batteries, do not make mistakes when using them so as not to damage the circuit. You can know its type and rated voltage by being familiar with the CR and ER in the model. When purchasing new batteries, you must buy them according to the original model, otherwise it will affect the performance of electronic products.

Rechargeable lithium batteries

There are many rechargeable lithium batteries, such as lithium-vanadium oxide batteries, lithium-ion batteries, and newly developed lithium-polymer batteries. Only the first two types are introduced here, focusing on lithium ion batteries.

Rechargeable lithium-ion batteries are currently the most widely used batteries in mobile phones, but they are more "delicate" and can not be overcharged or overcharged during use (which can damage or scrap the battery). Therefore, there are protective components or protective circuits on the battery to prevent expensive battery damage.

Lithium-ion batteries require high charging requirements. To ensure that the termination voltage accuracy is within 1 %, major semiconductor device plants have developed a variety of ICs for lithium ion battery charging to ensure safe, reliable and rapid charging.

Mobile phones are now very common. Some of them are nickel-metal hydrogen batteries, but smart phones are lithium-ion batteries. The correct use of lithium-ion batteries is very important for extending battery life.

1. Lithium-vanadium oxide batteries (Li-V6O13)

Lithium-vanadium oxide batteries consist of lithium as an anode, vanadium oxide as a cathode, and organic solvents of inorganic salts as electrolytes. It is characterized by charging. Taking battery No. 2 as an example, the lithium-vanadium oxide batteries are compared with lithium-manganese dioxide batteries and Lithium-thionyl chloride cells as shown in table 5.

As can be seen from table 5, since the rated voltage of the lithium-vanadium oxide battery is only 2.8 V and the rated capacity is also small, its specific energy is the smallest compared to the other two lithium batteries. The main parameters of this type of cylindrical battery are shown in table 6. As can be seen from table 6, the number of charges (cycle life) is not long, so this rechargeable battery was soon replaced by a lithium-ion battery.

2. Li-ion batteries (Li-Ion)

Lithium-ion cells are the most widely used lithium cells at present. They can be made into flat rectangular, cylindrical, rectangular and button-type batteries according to the requirements of different electronic products, and have batteries composed of several cells in series.

The rated voltage of lithium-ion batteries is 3.6 V (some products are 3.7 V). The end charging voltage at full charge is related to the battery anode material: the anode material is 4.2 V of graphite; The anode material is 4.1 V of coke. The internal resistance of different anode materials is also different. The internal resistance of the coke anode is slightly larger, and the discharge curve is also slightly different, as shown in Figure 1. Generally referred to as 4.1 V lithium ion batteries and 4.2 V lithium ion batteries. The termination discharge voltage of a lithium-ion battery is 2.5 V to 2.75 V (the battery plant gives a range of operating voltage or gives a termination discharge voltage, with slightly different parameters). Continuing discharge below the termination discharge voltage is called overdischarge, and overdischarge will cause damage to the battery.

Lithium-ion batteries are not suitable for large current discharges. Excessive current discharges will reduce the discharge time (the interior will produce higher temperatures and lose energy). Therefore, the maximum discharge current given by the battery production plant should be less than the maximum discharge current in use.

Lithium-ion batteries have certain temperature requirements. The factory gives the charging temperature range, discharge temperature range and preservation temperature range.

Lithium-ion batteries require very high charging requirements. It requires sophisticated charging circuits to ensure the safety of charging. The tolerance difference of the termination charging voltage accuracy is ± 1 % of the rating (for example, a lithium ion battery charged with 4.2 V has an tolerance difference of ± 0.042 V), and overvoltage charging will cause permanent damage to the lithium ion battery. Lithium-ion battery charging current should be based on the recommendation of the battery production plant and require a finite-current circuit to avoid overflowing(overheating). The commonly used charging rate is 0.25 C to 1C(C is the battery capacity, such as C = 800mAh, and 1C charging rate is 800mA). When charging a large current, the battery temperature is often detected to prevent overheating from damaging the battery or causing an explosion.

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