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The Cycle Life Of Lead Acid Battery
- Aug 14, 2018 -

Foreword

The factors affecting the life of lead-acid batteries are various, including the internal factors of the battery, such as battery structure, positive and negative grid materials, positive and negative active materials, separators, electrolyte concentration, etc., and also depend on a series of external Factors such as discharge current density, temperature, depth of discharge, maintenance conditions, and storage time. The deeper the discharge, the shorter the service life. Overcharging also shortens the life. As the acid concentration increases, battery life decreases. In the research process of large-capacity lead-acid batteries, we found that the lead-slip short circuit is an important cause of battery performance degradation and failure. In addition, the corrosion deformation of the positive grid, the positive active material shedding, softening, irreversible sulfation, and the serious accumulation of cerium on the active material are all key factors affecting the life of the battery.

In order to prevent corrosion of the positive grid, a multi-component low tantalum alloy was developed. The corrosion resistance of this multi-alloy is greatly improved. The negative grid is made of lead-plated copper. The ratio of the weight of the copper grid to the active material is 1:3, and the specific energy of the reservoir is significantly improved. Moreover, due to the good electrical performance of the copper grid negative electrode, the charging acceptance capability is strong, and the battery charge and discharge cycle life is raised. Adding additives to the positive and negative active materials improves the utilization rate of the active materials and prolongs the service life. In order to prevent the lead-free short circuit, a comprehensive short-circuit prevention measures are taken. High performance boards and a range of new assembly processes are used.

Introduction to the development of lead-acid batteries

The lead-acid battery was first produced by Gastron Prandt in 1860 and has a history of more than 140 years. Over the past 100 years, with the development of science and technology, the process, structure, mechanization and automation of lead-acid batteries have been continuously improved, and the performance has been continuously improved. Due to its excellent performance and price ratio, the production and application of lead-acid batteries are still at the top of various chemical power sources until today. The applications include power, start-up, emergency and working power, including vehicles, ships, aircraft, and telecommunications. Systems, computers, instruments and other equipment and facilities, especially in automotive batteries and industrial batteries, lead-acid batteries account for more than 90% of the market share, with an absolute advantage. 121. The original Valta stack appeared for the first time in 1800. Gotti 1801 Roth has observed the so-called "secondary current", that is, the current opposite to the direction of the charging current can be obtained after charging. Della·Weiwei studied the primary battery of Pb02 as a positive electrode in sulfuric acid solution from 1836 to 1843. Several electrode forms of the acid battery and the manufacturing process of the main process were gradually determined in the half century from 1860 to 1910. The earliest appeared was the forming plate. In 1881, Fore first proposed the paste plate. Xielang first used Pb.sb alloy casting grids to improve the fluidity of liquid alloys and the hardness in solid state. 1924 R Rendaojin invented the ball mill and replaced the red and yellow powder with the ball powder as the active material of the battery. The use of lignin as the negative electrode active material additive effectively prevented the lead sulfate crystal from becoming thicker and prolonged the life of the battery. It appeared in the 1920s. Microporous rubber separators, resin-paper separators in the 1940s, which gradually replaced wood partitions. During the 20 years from the 1950s to the 1960s, there were several major advances in the manufacturing process for lead-acid batteries: Plastic instead of hard rubber to make battery slots and covers; use thin plates and improve grid design; use in wall welding technology for start-up batteries; generally use low- or no-rhenium alloy cast grid; improve short-time discharge The utilization rate of active materials; the manufacturing process of dry-type batteries. After the 1970s, countries have vigorously developed maintenance-free and sealed lead-acid batteries. In basic theory, the achievements and means of physics, especially electronics, are widely adopted: Potentiometer, scanning current meter, scanning electron microscope, x. ray and neutron diffraction, nuclear magnetic resonance and electronic spectroscopy, etc. plus rotating disk electrode and meter Technical research focus from thermodynamics to the electrode kinetics.

The main producers of lead-acid batteries are distributed in several developed countries including the United States, Europe (UK, Germany, France, etc.) and Japan, and their total output accounts for about 70% of the world's total output. The United States has EXIDE Technologies, the world's largest producer of lead-acid batteries (with annual global sales of $2.8 billion), and other very large lead-acid battery manufacturers such as JOHNSON, CONTROL, DEKA, and DELPHI. The output value of lead-acid batteries in the United States accounts for about 20% of the world's total. However, in recent years, with the changes in factors such as technology and labor costs, some lead-acid battery companies have experienced a decline. The production of lead-acid batteries is transferred to countries such as India, Southeast Asia and other countries where labor costs are low. Europe has many large lead acid battery manufacturers, such as CHLORIDE, HOPPECKE, F1AMM, DETA, HAWKER and so on. Lead-acid batteries in Europe play an important role in the world, with a well-established technology-leading lead-acid battery manufacturer such as Sunshine (now a subsidiary of EXIDE). In 2001, the output of lead-acid batteries in Europe was 48.1 million, and in 2002 it was estimated to be 49.1 million. In 2005, it will reach 51.8 million. In terms of industrial batteries, in 2000, the number of spare batteries was 130,000, the number of sealed batteries less than 24 Ah was 110,000, and the number of sealed batteries larger than 24 Ah was 430,000. The producers of lead-acid batteries in Japan mainly include Yuasa Battery Co., Ltd., Matsushita Battery Co., Ltd., Furukawa Battery Co., Ltd., Shin-Kobe Electric Co., Ltd., and Japan Battery (GS). According to relevant statistics, in 2002, the output value of lead-acid batteries in Japan was about 1.16 billion US dollars, the starting batteries of lead-acid batteries accounted for 55.7%, and the industrial batteries (fixed lead-acid batteries) accounted for 6.7%. The battery accounts for 8. O%, the other accounted for 29.7%. Since the 1990s, the proportion of lead-acid batteries in the total output value of secondary batteries has remained at around 20%, and has increased in recent years.

In recent years, the performance of lead-acid batteries in China has been greatly improved, and the energy of weight ratio and volume ratio have been greatly improved. Less maintenance and maintenance-free, valve-regulated sealed lead-acid batteries are growing rapidly.

 

Lead-acid battery structure, composition and classification

The electrochemical expression of a lead-acid battery is: (1) PbIH2SO·IPb02(+).

The main structure of the lead-acid battery includes a positive electrode, a negative electrode, a separator, a sulfuric acid electrolyte, a battery tank, and a cover. The positive and negative electrodes are respectively welded into a pole group, and the large-capacity battery is led out from the bus bar to form a pole. The electrolyte used in lead-acid batteries is a certain concentration of sulfuric acid electrolyte. The function of the rain separator is to separate the positive and negative electrodes. It is an electrical insulator (such as rubber, plastic, fiberglass, etc.), resistant to sulfuric acid corrosion, oxidation resistant, and has sufficient porosity and pore size to allow electrolyte and The ions pass freely. The tank body is also an electrical insulator, which is resistant to acid and temperature, and has high mechanical strength. Generally, hard rubber or plastic is used as the tank body.

1.2.1 Positive active material

The positive electrode active material is lead dioxide. The crystal forms of Pb02 are d--Pb02 and 0--Pb02. In a sulfuric acid solution,

The Pb02 electrode reaction is:

PbOa+HS04"+3H++2e=PbS04+2H20

Tests have shown that the discharge capacity of B-Pb02 is always greater than the discharge capacity of a--Pb02. This is because the true specific surface area of B-Pb02 is larger than that of Q--Pb02, which directly affects the growth and diffusion of lead sulfate on its surface, thus affecting the utilization rate of active substances. During charge and discharge, n--Pb02 and B-Pb02 are transformed into each other, mainly a--Pb02 is converted to 13--Pb02. The charge and discharge reaction mechanism of the positive electrode can be divided into a dissolution deposition mechanism and a solid state mechanism.

In order to improve the utilization ratio of the active material of the positive electrode, various additives, including conductive additives, inorganic additives such as barium, calcium sulfate, aluminum sulfate, zeolite, and the like, and organic and polymer additives are used. Wei Guolin believes that the BD additive can greatly improve the battery capacity. Significantly improve the utilization rate of active materials, and form a microstructure with more pores, thereby improving the mass transfer process and significantly improving the charge and discharge performance of the positive electrode. The combination of BD and PII can significantly increase the battery capacity and the utilization rate of the positive active material.

Ramanthanll41 research shows that calcium sulfate is added to the positive active material to improve battery performance at high discharge rates and low temperatures. The addition of RS03H to the positive electrode active material improves the diffusion condition of H+ in the positive electrode micropores, and greatly increases the positive electrode discharge capacity and the positive electrode active material utilization rate 115. D. Pavlov and N. CopkOV mixes Pb, 04 and lead powder, and obtains 4PbO·PbS04 paste as a positive electrode after high temperature curing. The cycle life of the battery is increased by 30% because of a in the active material. The content of Pb02 is significantly increased by I". Document 1171 introduces a high-performance positive electrode plate with persulfate added to the common lead paste composition, the active material has high porosity and specific surface area, and the discharge power is at least 1 W/cm2. The material has a porosity of 55% and a specific surface area of at least 4 m2/g. The literature [181 proposes to add PbF2 to the lead paste and add fluororesin latex as a binder, which does not require curing, which is beneficial to the high power output of the battery. It is proposed to use propylene and propylene styrene while adding carbon to the active material, which is mainly beneficial to the formation of a network and increases the porosity.

1.2.2 Negative active material

The negative electrode active material is lead. When the battery is discharged, the lead anode is an anode, and the lead is oxidized to Pb", which diffuses from the surface of the electrode into the solution, and a precipitation reaction occurs with the 8042. If the lead electrode is overpotential enough to cause solid phase nucleation, a solid phase reaction may occur. S042 directly collides with lead to form solid lead sulfate, and Pb2+ is reduced during charging. Lead can be passivated in sulfuric acid solution. In order to prevent this from happening, sponge lead is used as a negative electrode in production.

In order to improve battery life and capacity and suppress hydrogen evolution reaction, it is necessary to add various expansion agents to the negative electrode. The negative electrode lead is easily oxidized in the drying step after the formation, and a corrosion inhibitor can be added. Commonly used expansion agents are inorganic expansion agents and organic expansion agents. Inorganic expansion agents include barium sulfate, barium sulfate, carbon black, etc., which facilitate the diffusion of the electrolyte, facilitate deep discharge, delay the passivation, and prevent the specific surface area of the electrode from shrinking. The organic swelling agent includes humic acid, lignin, lignosulfonate, and synthetic tanning agent, and functions to prevent the specific surface area of the electrode from shrinking. Common anti-oxidation inhibitors are a-hydroxy B-naminic acid, glycerin, xylitol, ascorbic acid, rosin, etc., all of which can inhibit lead oxidation.

1.2.3 battery electrolyte

The battery electrolyte is sulfuric acid. Na2SO was added to the electrolyte at a concentration of 0.7 mol/L. The capacity of the battery is significantly increased. CoSO. It is also an additive that people have studied a lot. CoSO is added to the lead battery electrolyte. The adhesion between the positive active material and the grid and the adhesion between the Pb02 particles can be improved, which effectively improves the cycle life of the positive grid. The (NH4)2Cr207 electrolyte additive can increase the capacity of the lead electrode, accelerate the cathode and anode processes of the electrode, and increase the oxygen evolution overpotential. In addition, the addition of nicotinamide, hydroxylamine compounds, and unsaturated aliphatic compounds is also beneficial to the life of the battery.

1.2.4 grid

The battery active material is usually fixed to a grid made of lead and lead alloy. Lead-bismuth alloy is the grid alloy that was invented earlier, and the content of antimony still widely used is 4 to 6%. Compared with pure lead, lead-bismuth alloy has good mechanical properties, good castability, low thermal expansion coefficient and uniform corrosion. The disadvantages of lead-bismuth alloys are large electrical resistance, high gassing rate, increased water loss of the battery, and accelerated corrosion of the grid. To this end, it is necessary to reduce the niobium content to form a low niobium alloy and an ultra low niobium alloy. Low-ruthenium alloys mainly need to solve the thermal cracking phenomenon in grid casting. Therefore, it is necessary to add a nucleating agent. The nucleating agents are mainly s, Se, cu and As. The main low-lying alloys are silver-containing and antimony-barium alloys; selenium- and sulfur-containing low-bismuth alloys; lead-bismuth-arsenide, lead-cadmium-cadmium and lead-cadmium-silver alloys; lead-calcium-tin-aluminum alloys;

1.2.5 partition

The separator is one of the components of the battery, its main role is to prevent short circuit between positive and negative. However, it does not significantly increase the internal resistance of the battery, but also allows the electrolyte to diffuse freely and ionize. In addition, it must have certain mechanical strength, acid corrosion resistance and oxidation resistance. The main types of separators are microporous rubber separators, sintered polyvinyl chloride microporous plastic separators, polyvinyl chloride flexible plastic separators, glass fiber and polypropylene separators, glass filament separators and composite separators.

1.2.6 Classification

Lead-acid batteries are customarily used in three classifications.

 

1) Classified by purpose

China's lead-acid battery products are classified according to their use. Mainly divided into starting, fixed, power and other aspects. The starting battery is mainly used for various automobiles, locomotives, ship starting and lighting. It is required to discharge at a large current, can start at a low temperature, the internal resistance of the battery should be small, and the positive and negative plates should be thin. The fixed lead-acid battery is mainly used as a backup power source for various large-scale equipment systems, the plate is thick, the electrolyte is thin, and the service life is long. The power battery mainly provides power for various power systems, and the long-term and short-time performance requirements are better.

2) Classification by plate structure

Mainly divided into paste, tube, and formation. The lead oxide is adjusted into a lead paste with a sulfuric acid solution, coated on a grid cast with a lead alloy, and dried and formed into a paste-like plate. The skeleton is made of lead alloy, and the fibrous tube is prepared in the skeleton outer casing, and the tube is filled with an active material. This electrode plate is called a tubular plate. Plate by pure lead

Casting is called forming.

3) Classification according to electrolyte and charge maintenance

Mainly divided into dry discharge battery, dry charge battery, wet charge battery, maintenance-free, less maintenance battery, valve-controlled sealed battery.

In 1880, Gladstone and Tribo proposed the "bipolar sulfate theory" for the reaction of lead-acid batteries, which believed that both the positive and negative electrodes produced lead sulfate when the battery was discharged:

Positive electrode reaction Pb02+4H++S042-+2e=PbS04+2H20

Negative electrode reaction Pb+S042”-2e=PbS04

The total reaction of the battery Pb02+Pb+2H2S04=2PbS04+2H20

Electromotive force, open circuit voltage, working voltage

The electromotive force of the battery is the difference between the equilibrium electrode potentials of the two electrodes. The battery electromotive force is a function of the concentration of sulfuric acid. The open circuit voltage of the battery is the potential difference between the electrodes when no current flows through the external circuit, and is generally smaller than the battery electromotive force, which is directly related to the state of charge of the battery. The operating voltage of the battery, also known as the discharge voltage or load voltage, refers to the potential difference between the two poles of the battery when there is an external current. The operating voltage is always lower than the open circuit voltage because the resistance caused by the polarization resistance and the ohmic resistance must be overcome when the current is passed through the interior of the battery. As the discharge of the battery progresses, the positive and negative active materials and sulfuric acid are gradually consumed, the amount of water increases, the acid concentration decreases, and the voltage of the battery decreases.

The battery capacity refers to the amount of electricity discharged from the battery. It is expressed in ampere-hours and is divided into theoretical capacity, actual capacity and rated capacity. The capacity of the battery is related to the amount of active material and its utilization. In addition, the capacity of the battery is not a fixed value, it is directly related to the discharge rate, temperature, termination voltage, battery discharge capacity (or discharge time) and discharge current I. In 1898 Peukert proposed that the equation K=tP is widely use. The larger the discharge current, the smaller the depth of action, the lower the utilization of the active material, and the smaller the capacity of the battery. The battery capacity decreases with decreasing temperature, which is closely related to the temperature having a serious influence on the viscosity and resistance of the electrolyte.

The energy that can be output by the battery under certain conditions is called the energy of the battery, which is generally indicated by Wh. The actual energy of the battery is always lower than its theoretical capacity, which is mainly determined by the utilization of the active material. Actual energy of the battery = capacity · average voltage. The energy given by a unit mass or unit volume of the battery is the mass ratio energy or volume ratio energy. It is closely related to the total amount of active material of the battery electrode, the utilization rate of the active material, the structure of the battery, the manufacturing process of the battery, and the working condition of the turbidity. The lead-acid battery will have different battery specific energy under different temperatures, stirring system air flow rate and different battery discharge rates. When the temperature rises, the battery electromotive force increases, the electrode reaction speed increases, and the internal resistance of the battery decreases. The battery ratio can be increased. However, the increase in temperature will affect the corrosion rate of the grid and the performance of the battery separator. Therefore, the operating temperature of the battery should be controlled within a certain range. Increasing the air flow rate of the agitation system is beneficial to reduce the hydrogen content in the battery and prevent delamination of the electrolyte, thereby improving battery performance. The higher the discharge rate, the larger the discharge current, the more uneven the current distribution on the electrode, and the current is preferentially distributed on the surface closest to the main electrolyte, so that the lead sulfate on the outermost surface of the electrode preferentially forms the pore of the porous electrode. The electrolyte does not sufficiently supply the internal reaction of the electrode, and the platinum inside the electrode cannot be fully utilized, so that the specific energy of the battery is lowered at high rate discharge.

The internal resistance of an alumina battery is mainly composed of an electrolyte, a separator, a plate, and a pole. The internal resistance of the battery is not constant, and it changes continuously with time during the charging and discharging process because the composition of the active material, the electrolyte concentration and the temperature are constantly changing. The internal resistance of lead-acid batteries is very small, which can be neglected when discharging small currents, and the voltage drop can reach hundreds of millivolts when discharging large currents. In addition, the battery's charge retention capability and low temperature charge acceptance are also important manifestations of the overall performance of the battery.

The service life of lead-acid batteries is one of its important performance indicators. The life of a battery is generally expressed in cycles. The battery undergoes a charge and discharge, which is called a cycle. In a certain charging and discharging system or working mode, the number of cycles that the battery is subjected to before the battery capacity drops to the specified value is called the service life, that is, the battery life. Life can also be expressed in terms of time of use. In practical applications, battery life has a variety of expressions such as bench test period, assumed period, and actual use time, which are mainly determined by the way the battery is used. Factors affecting battery life include the internal factors of the battery, including the structure of the battery, the material of the grid, the performance of the active material, etc., and also depend on a series of external factors such as discharge current density, temperature, depth of discharge, maintenance status and storage time. Wait. The deeper the discharge depth, the shorter the service life. Overcharging also shortens the life. Battery life is extended with increasing temperature. As the acid concentration increases, battery life decreases. The internal factors of the battery affect its service life mainly in the following aspects.

In the research of large-capacity lead-acid batteries, we found that the lead-slip short circuit is an important cause of battery performance degradation and ultimately failure. During the recycling of the battery, the active material and the fiber additive on the positive and negative plates are detached, a part of which is present in a solid form, and a part of which is dissolved in the electrolyte. As the charge and discharge process progresses, the dissolved material is reduced and precipitated in the negative electrode, and the undissolved substances and additives can also be precipitated in the positive and negative plates and other places in the polar group. As time elapses, the battery charge and discharge cycle increases, more and more substances are deposited, and eventually the positive and negative electrodes are locally connected, resulting in a micro short circuit, called a lead short circuit. The short-circuit point increases self-discharge and the temperature rises. With the accumulation of time, the lead short-circuit area is increased, the charging efficiency is greatly reduced, the battery capacity is decreased, and the hydrogen evolution amount is increased. Moreover, the local high temperature may cause the separator to burn through, lose the isolation effect, and the positive and negative electrodes are connected in one body, the structure is damaged, the function is lost, and finally the battery life is terminated.

The positive grid is oxidized to lead sulfate and lead dioxide due to electrochemical corrosion during the charging process, resulting in a decrease in strength, a decrease in electrical conductivity, and eventually a large deformation. Partial short circuit will also cause corrosion of the II speed positive plate, severe decay, active material falling off, and "F pole function loss." Sun Yusheng [41] and other researches also believe that the main reasons for the failure of VRLAB are: corrosion and growth of the positive grid, the shrinkage of the negative active material and the reduction of porosity and the degradation and loss of the negative organic expander.

n-Pb02 is the skeleton of the active substance due to a. Pb02 is gradually converted into B-Pb02, so that the network is weakened and destroyed, eventually leading to softening and shedding. 70's SimonA. C. , Aulder S. M. Coral structure model was established with CangT G et al. It is believed that there are two sizes of pores in the positive electrode material. The structure of the pores is re-adjusted with the charge and discharge cycle, the pores become large pores, and the particles are dense. After a certain degree, It will fall off and the electrode will fail.

 

Irreversible sulfation

This is mainly due to the over-discharge of the battery, which causes the anode to generate PbS04 crystal which is difficult to invert. In severe cases, the electrode is ineffective and the charging acceptance is reduced. The positive self-discharge leads to loss of active material capacity and causes irreversible precipitation of lead sulfate, which eventually leads to electrode damage. Hu Xinguo [43] believed that CdSO was added to the battery electrolyte. The plate can be inhibited from sulfation, and the effect is remarkable.


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