Why is the mobile phone battery less durable the more you use it?

When I was playing with my mobile phone, I found that the battery of the mobile phone was fleeting, which made me have to sigh and turn around to find the charger.

Why are our phones becoming less and less used? It starts with our batteries.

An early product of mobile phone batteries

In 1973, the world's first mobile phone was born at Motorola Labs[1]. This phone is very bulky, but thanks to the built-in nickel-cadmium battery, this phone can be separated from the complicated electronic circuits to achieve real-time mobile calls.

As the first battery built into a mobile phone, nickel-cadmium batteries are themselves bulky. In the last century, the popular "big brother telephone" mostly used nickel-cadmium batteries. Nickel-cadmium batteries have low capacity and contain highly toxic cadmium, which is not conducive to the protection of the ecological environment. And nickel-cadmium batteries also have a very obvious memory effect: if the power is not completely drained before charging, it will cause a decrease in battery capacity over time.

Basic structure of nickel-cadmium battery[2]

In 1990, Japan's Sony Corporation was the first to develop a nickel-metal hydride battery. Compared with its old-timers, nickel-metal hydride batteries can not only be made thinner, but also effectively improved in capacity [3]. The advent of nickel-metal hydride batteries has made mobile phones more portable, and mobile phones can support longer calls. Therefore, with the advent of nickel-metal hydride batteries, bulky nickel-cadmium batteries were gradually replaced, and small mobile phones became popular. But nickel-metal hydride batteries still have a memory effect, which is why the previous generation of mobile phones need to be fully discharged and then recharged. Moreover, due to the limited energy density of nickel-cadmium batteries, mobile phones at that time could only support relatively simple tasks such as making calls, and there was still a big gap from our current smartphone form.

The rise of lithium batteries

Lithium metal was discovered in the nineteenth century. Because lithium has a relatively low density, high capacity and relatively low potential, it has unique advantages as a galvanic battery. However, lithium is a very active alkali metal element, resulting in the preservation, use or processing of lithium metal environmental requirements are very high, and are much more complex than other metals. Therefore, in the process of studying lithium batteries with lithium as electrode materials, scientists have overcome many research problems through the continuous development and improvement of lithium batteries, and finally made it what it is today.

Lithium batteries using lithium metal as the negative electrode were the first to be commercialized. In 1970, Japan's Panasonic invented the lithium fluorocarbon battery, which has a large theoretical capacity, stable discharge power, and small self-discharge phenomenon. However, this type of battery cannot be charged and belongs to a primary lithium battery [2].

In the 70s of the 20th century, Stanley Whittingham, a developer from ExxonMobil, was the author of the company. Stanley Whittingham proposed the principle of battery charge and discharge of ion intercalation and published a patent for lithium titanium disulfide batteries in 1975. In 1977, the Whittingham team working for Exxon developed a secondary battery with aluminum-lithium alloy Li-Al as the negative electrode and titanium disulfide TiS₂ as the positive electrode, in which the aluminum-lithium alloy can improve the stability of lithium metal and enhance the safety of the battery [2]. During the discharge process, the electrochemical processes that occur in the battery are:

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Positive: xLi+ + TiS₂+ xe- → LixTiS₂

Among them, TiS₂ is a layered compound, and the interaction between layers is a weak Van der Waals Force (Van der Waals Force), and lithium ions with a smaller volume can enter the layers of TiS₂ and undergo charge transfer, and store lithium ions, similar to squeezing jam into a sandwich, this process is the intercalation of ions [4][5]. During discharge, Li+ ions in the electrolyte are inserted between the TiS₂ layers of the positive electrode, accepting a charge and forming LixTiS₂.

Structure of TiS₂ and principle of intercalation reaction during discharge[6]

The secondary lithium batteries at this stage mainly use metal lithium as the anode material, and improve the life and safety of the battery by improving the cathode material. As the earliest secondary lithium battery to achieve commercialization, the use of lithium metal as the anode material has a low negative potential, high energy density of the battery, and is more portable, but its safety has also been widely questioned. In the late spring of 1989, the explosion of the first generation of lithium metal batteries produced by the Canadian company Moli Energy also brought the commercialization of lithium metal batteries to a standstill [2].

In order to improve the safety of lithium batteries, the development of new electrode materials is very important for lithium batteries. However, using other lithium compounds as negative electrodes instead of lithium will increase the negative electrode potential, reduce the energy density of lithium batteries, and reduce battery capacity. Therefore, finding suitable new electrode materials has also become a difficult problem in the field of lithium battery research.

Around 1980, John Bannister Goodenough, who taught at the University of Oxford in the United Kingdom, and others discovered the compound lithium cobalt oxide LiCoO₂ (LCO), which can hold lithium ions. LiCoO₂ had a higher potential than other cathode materials at the time. This enables lithium batteries with LiCoO₂ as the positive electrode to provide higher voltages with higher battery capacity. [7] [8]

Schematic diagram of lithium cobalt oxide crystal structure[9]

Lithium cobalt oxide crystals are layered and belong to the hexagonal crystal system. Among them, the octahedral lattice composed of O and Co atoms is arranged in a plane into a CoO₂ layer, and the CoO₂ layer is separated by lithium ions, and forms a planar lithium ion transport channel. This allows lithium cobalt oxide to transport lithium ions relatively quickly through planar lithium ion channels. The detachment and intercalation process of lithium ions in lithium cobalt oxide is similar to an intercalation process. During the mild charge-discharge process, lithium cobalt oxide can maintain the stability of the crystal structure. However, with the gradual removal of lithium ions, lithium cobalt oxide has a tendency to shift to a monoclinic crystal system [2]. In lithium batteries with lithium cobalt oxide as the positive electrode, the reaction that occurs at the positive electrode during the discharge process is:

Positive electrode: Li1-xCoO₂ + xLi+ + xe- → LiCoO₂

Intention of lithium ions in lithium cobalt oxide during discharge[9]

Compared with titanium disulfide, lithium cobalt oxide cathode material has a high cathode potential, and the layered structure lithium cobalt oxide can transport lithium ions faster, which is an excellent cathode material for lithium-ion batteries.

In the same year, Rachid Yazami discovered the cyclable ion intercalation of lithium ions in graphite and verified the feasibility of graphite as a cathode for lithium batteries [10]. Graphite has a lamellar structure, and similar to TiS₂, the middle layers of graphite are connected by weak van der Waals forces, which allows smaller lithium ions to enter the graphite layers and undergo charge transfer.

Graphite has a layered structure, and the layers are interconnected by van der Waals forces [11]

In a 1983 paper [12], Yazami used polyethylene oxide-lithium perchlorate solid-state electrolysis, and used lithium metal as the negative electrode and graphite as the positive electrode to form a galvanic cell. During the discharge process, the graphite as the positive electrode reacts as follows:

nC + e- + Li+ → (nC, Li)

Subsequent occurrence: (nC, Li) → LiCn

During the discharge of galvanic cells with graphite as the positive electrode, lithium ions undergo an intercalation reaction in the graphite layer, where charge transfer occurs and the compound LiCn is formed.

The arrival of lithium-ion batteries

In 1982, Yoshino Akira, who worked for Asahi Kasei Corporation in Japan, used lithium cobalt oxide as the cathode and polyacetylene (C2H2)n as the anode to construct a sample of lithium-ion batteries [13]. During the discharge process of lithium cobalt oxide battery, lithium ions migrate from the positive electrode of the battery to lithium cobalt oxide through the electrolyte to realize battery discharge.

However, lithium cobalt oxide batteries still have many problems. The negative polyacetylene of the battery has a low energy density and low stability. Therefore, Akira Yoshino adopted a new graphite-like material "soft carbon" instead of polyacetylene as the anode material for batteries, and in 1985, the first lithium-ion battery prototype was prepared and patented[10]. The lithium-ion battery prototype, designed by Akira Yoshino, became the prototype of many modern batteries.

Schematic diagram of lithium-ion battery discharge, lithium-ion migration process

Compared with lithium batteries, the galvanic battery designed by Yoshino Akira with carbonaceous material as the negative electrode and lithium cobalt oxide as the positive electrode gets rid of metal lithium, so this type of battery is also called "lithium-ion battery". Because in lithium cobalt oxide lithium-ion batteries, lithium ions undergo intercalation reactions at both positive and negative electrodes, and rapid charge transfer is achieved through rapid intercalation of lithium ions, so this battery structure is also figuratively called rocking chair battery.

In 2019, the Nobel Prize in Chemistry was awarded to American scientist John M. John B. Goodenough and British scientist Stanley Whittingham Stanley Whittingham) and Japanese scientist Akira Yoshino in recognition of their research contributions to lithium-ion batteries [4].

Nobel Prize winners: From left to right, American scientist John M. John B. Goodenough, British scientist M. Stanley Whittingham and Japanese scientist Akira Yoshino [4]

The emergence of lithium-ion batteries with carbon materials as the negative electrode and lithium cobalt oxide as the positive electrode has promoted the development of lithium-ion batteries. With the deepening of researchers' research on lithium-ion batteries, three systems have been developed for the cathode materials of lithium-ion batteries: lithium cobalt oxide (LCO), lithium iron phosphate (LFP) and ternary nickel-cobalt-manganese (NMC/NCM) systems. Among them, the lithium cobalt oxide system has a relatively higher battery capacity, and it has a pivotal position in the field of 3C electronic products such as mobile phones and computers that we usually use. The lithium iron phosphate system and ternary lithium system have higher stability, so they have a wide range of applications in new energy vehicles. [14]

The advent of lithium-ion batteries has completely changed the way we live. Compared with nickel-cadmium batteries and nickel-metal hydride batteries, lithium-ion batteries have a higher energy density, and lithium-ion batteries with the same battery capacity are more portable and can support the high power consumption of smartphones with integrated rich functions. At the same time, most lithium-ion batteries have no memory effect and do not need to be fully discharged and recharged, so lithium-ion batteries can be charged on demand. Compared to lithium batteries, the charging rate of lithium-ion batteries is significantly improved. And the charging rate of lithium-ion batteries is fast, which greatly facilitates our lives. Therefore, in application scenarios such as mobile phones, mobile computers, and new energy vehicles, lithium-ion batteries have gradually replaced nickel-cadmium batteries and nickel-metal hydride batteries in some scenarios with their excellent performance.

Why phone battery life

The more you use it, the shorter it gets?

1

The pain of nickel-cadmium batteries - memory effect

For nickel-cadmium batteries, the grains of the negative cadmium of the nickel-cadmium battery prepared by sintering are thicker, and when the nickel-cadmium battery is not completely charged and discharged for a long time, the cadmium grains are prone to aggregation and aggregation. At this time, a secondary discharge platform is formed when the battery is discharged. The battery will use this stage discharge platform as the end point of battery discharge, the capacity of the battery becomes low, and the battery will only remember this low capacity in the subsequent discharge process [15]. This is why older generations of mobile phones with nickel-cadmium batteries are often suggested to need to be fully discharged before charging. However, with the continuous improvement of the processing technology of nickel-cadmium batteries and nickel-metal hydride batteries, the impact of memory effect on battery capacity has been continuously reduced, and the harm of complete charging and discharging to battery life has gradually emerged.

Source: Pixabay

Nickel-cadmium batteries have a significant memory effect, while lithium-ion batteries have almost no memory effect. And because the energy density of lithium-ion batteries is higher than that of nickel-cadmium batteries, lithium-ion batteries are mainly used in our mobile phones, computers and other products. Therefore, when we use smartphones or computers equipped with lithium-ion batteries on a daily basis, we do not need to worry about the memory effect of the battery.

2

Overcharging and discharging lithium-ion batteries leads to life degradation

Lithium cobalt oxide has a high theoretical capacity, but the actual capacity of lithium cobalt oxide in our use is far from reaching the theoretical capacity. Because after we charge and discharge lithium-ion batteries beyond this capacity, lithium cobalt oxide will undergo an irreversible charging and discharging process, which is what we often call battery overcharge or overdischarge. This process is accompanied by a structural phase change of lithium cobaltate, which reduces the capacity of the battery.

Schematic diagram of six-direction monoclinic phase transition of lithium cobalt oxide[16]

When the battery is overcharged, a large number of lithium ions are removed from the negative electrode lithium cobalt oxide of the lithium-ion battery, and the remaining lithium ions are not enough to support the original structure of lithium cobalt oxide, resulting in the transformation of Li1-xCoO₂ crystals from hexagonal crystal system to monoclinic crystal system, and the original hexagonal structure collapses without ion support. In this process, the phase transition of lithium cobalt oxide is not completely reversible, and the unit cell parameters of lithium cobalt oxide change, stress changes, and lithium ion vacancies are compressed, resulting in the capacity of lithium-ion batteries. [17] [18]

3

Instability of high-voltage lithium-ion batteries

In addition to the irreversible change of battery capacity caused by the structural phase change of lithium cobalt oxide, the increase of the output voltage of lithium-ion batteries also leads to other side reactions in lithium-ion batteries, and the life of lithium-ion batteries is decayed. At present, smartphones on the market usually use a charge and discharge voltage of around 4.4V[14]. High voltage can increase the capacity of lithium-ion batteries and speed up the charging and discharging rate of lithium-ion batteries. However, this is followed by a series of side effects such as the increase of side reactions on the electrode surface of lithium-ion batteries and the instability of the electrolyte at high voltage.

Influence mechanism of life attenuation of high-voltage lithium-ion batteries[18]

The lithium-ion battery electrolyte reacts at the solid-liquid interface of the positive and negative electrodes to form a passivation layer covering the surface of the electrode. This passivation layer has the characteristics of a solid electrolyte, and Li ions can be freely embedded and removed through this passivation layer, so this passivation film is called "solid electrolyte interface", referred to as SEI film [19]. The process of forming the SEI film consumes some lithium ions, causing irreversible losses in lithium-ion battery capacity. Under the action of high voltage, the side reactions on the surface of such electrodes are serious, so that the battery capacity gradually decreases.

What to pay attention to when using your phone

1

High temperature does not charge

Do not charge your phone when it overheats or has an extremely low temperature. When the mobile phone is overheated, charging the lithium-ion battery under high temperature conditions will also change the positive and negative structure of the lithium-ion battery, resulting in irreversible attenuation of battery capacity. Therefore, trying to avoid charging the mobile phone under too cold or too hot conditions can also effectively extend its service life.

2

Replace the battery in time

In the process of using digital products such as mobile phones, laptops or tablets, when we find that the battery back cover is deformed, the battery is bulging and other abnormalities, we should stop using it in time and replace the battery with the manufacturer, so as to avoid the safety hazards left by improper use of the battery as much as possible.

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[3] Ni-MH-Ni batteries - Zhihu https://zhuanlan.zhihu.com/p/630028868

[4] The Nobel Prize in Chemistry 2019. NobelPrize.org. Nobel Prize Outreach AB 2023. Sun. 13 Aug 2023.

[5] Binghamton professor recognized for energy research https://www.rfsuny.org/rf-news/binghamton-energy/binghamton---energy.html

[6] Hongwei,Tao,Min,et al. TiS2 as an Advanced Conversion Electrode for Sodium-Ion Batteries with Ultra-High Capacity and Long-Cycle Life. [J]. Advanced Science, 2018.

[7] Lithium-ion battery Wikipedia https://en.wikipedia.org/wiki/Lithium-ion_battery

[8] John B. Goodenough Facts https://www.nobelprize.org/prizes/chemistry/2019/goodenough/facts/

[9] Lithium Cobalt Oxide – LiCoO2，https://www.chemtube3d.com/lib_lco-2/

[10] Lithium-ion battery Wikipedia https://en.wikipedia.org/wiki/Lithium-ion_battery#cite_note-31

[11] Graphite Wikipedia https://en.wikipedia.org/wiki/Graphite

[12] Yazami R, Touzain P. A reversible graphite-lithium negative electrode for electrochemical generators[J]. Journal of Power Sources, 1983, 9(3): 365-371.

[13] Akira Yoshino Wikipedia https://en.wikipedia.org/wiki/Akira_Yoshino

[14] Introduction to contemporary lithium-ion battery systems Zhihu https://zhuanlan.zhihu.com/p/374494628

[15] Memory effect Baidu Encyclopedia https://baike.baidu.com/item/%E8%AE%B0%E5%BF%86%E6%95%88%E5%BA%94/1685065?fr=ge_ala

[16] Reimers J N , Dahn J R . Electrochemical and Insitu X-Ray-Diffraction Studies of Lithium Intercalation in Lixcoo2[J]. Journal of the Electrochemical Society, 1992, 139(8):2091-2097.

[17] Research progress of lithium cobalt oxide as a lithium-ion cathode material https://www.chemicalbook.com/NewsInfo_21664.htm

[18] Zhang Jienan. Failure analysis and modification study of high voltage lithium cobalt oxide[D]. University of Chinese Academy of Sciences,2018.

[18] Schlasza C , Ostertag P , Chrenko D ,et al. Review on the aging mechanisms in Li-ion batteries for electric vehicles based on the FMEA method [C] 2014 IEEE Transportation Electrification Conference and Expo (ITEC). IEEE, 2014

[19] Why is SEI film formed in lithium-ion batteries? What are the specific steps for SEI membrane generation? What is the structure of SEI membranes? Zhihu https://www.zhihu.com/tardis/bd/art/603133202?source_id=1001

Planning production

Author丨Institute of Physics, Chinese Academy of Sciences (ID: cas-iop)

Responsible editor丨Bai Li