CN114725549B - Method and apparatus for charging lithium metal battery - Google Patents

Abstract

The invention relates to a charging method and a charging device for a lithium metal battery, wherein the charging method is a first constant voltage charging and subsequent constant current-constant voltage coupling charging method, namely CV ₁ ‑CC‑CV ₂ Provided is a charging method. The charging method provided by the invention adopts constant voltage charging in the initial stage, and is essentially different from the initial constant current charging in the standard charging method. By utilizing the charging method, an initial constant voltage stage is introduced before a standard charging protocol, so that an internal electric field of the battery can be strengthened, lithium ions in the electrolyte are promoted to migrate to a negative electrode, and the rapid consumption of the interface lithium ions during rapid charging is slowed down.

Description

Charging method and charging device of lithium metal battery

technical field

The invention relates to the field of batteries, in particular to a charging method and a charging device for a lithium metal battery.

Background technique

Lithium-ion batteries are widely used in smart phones, notebook computers, electric vehicles and other fields, but with the development of society, the existing commercial lithium-ion batteries have been difficult to meet people's growing demand for ultra-long battery life and fast charging electronic products. demand. Metal lithium has an ultra-high theoretical specific capacity of 3860 mAh·g ^-1 (372 mAh·g ^-1 for graphite) and the lowest redox potential (-3.04 V relative to standard hydrogen potential), which can greatly improve the energy density of batteries. Active lithium metal has the characteristics of fast kinetic reaction, so it also has the application potential of fast charging. Based on this, lithium metal batteries using metal-containing lithium foils as negative electrodes are receiving increasing attention in the field of commercial batteries.

In fact, the commercial application of lithium metal batteries is earlier than the existing lithium ion batteries. In the 1980s, Moli Energy in Canada first launched a battery using lithium metal as the negative electrode. This battery also allowed Moli Energy to dominate the global battery market. , Since a large number of dendrites will be produced in the process of using lithium metal batteries, which are easy to cause explosions, in 1989, the lithium metal batteries suffered continuous fire and explosion accidents, resulting in a large-scale recall of the battery worldwide. Since then, the company that briefly dominated the global battery market has been stagnant and was eventually acquired by Japan's NEC Corporation. In 1991, Japan's Sony Corporation changed lanes first, using graphite material as the negative electrode to avoid the application of negative metal lithium, thereby avoiding the formation of lithium dendrites. At this point, lithium-ion batteries began to run wild, quickly leaving other types of batteries behind. After nearly 30 years of development, while the energy density and charging performance of lithium-ion batteries have been significantly improved, their development has also reached a bottleneck stage.

Lithium batteries generally refer to batteries containing lithium elements, including two categories: Lithium-ion batteries and Lithium metal batteries. In addition, lithium batteries also have other names such as lithium secondary batteries and lithium-based batteries. There are essential differences between lithium metal batteries and lithium ion batteries (Nature Nanotechnology, 2017, 12, 194). The essential difference between lithium ion batteries and lithium metal batteries lies in the negative electrode. The material of the negative electrode of lithium ion battery is carbon material (graphite, soft carbon and hard carbon, etc.) or silicon material, and the fundamental feature of lithium metal battery is that the material of the negative electrode adopts metal lithium or a composite containing metal lithium. The negative electrode materials of existing lithium ion batteries are carbon materials (graphite, soft carbon and hard carbon, etc.) or silicon materials, and lithium-containing compounds are used as positive electrode materials; while lithium metal batteries use metal lithium or a composite containing metal lithium. As the negative electrode material, the positive electrode adopts a positive electrode material with low working voltage. The low working voltage positive electrode material means that the positive electrode material has an electrode potential of less than or equal to 3 V relative to metal lithium (ie vsLi ⁺ /Li), such as titanium Lithium oxide (1.5V), organic lithium storage material (1.9 V), elemental sulfur (2.1V) or oxygen (2.8V), etc., and the use of lithium iron phosphate (3.4V), nickel-cobalt-manganese ternary material (3.8 V) , lithium cobalt oxide (3.9 V) or lithium manganate (4.0 V) and other high operating voltage commercial lithium-ion battery cathode materials are significantly different.

The charging and discharging process of a lithium-ion battery is the process of intercalation and deintercalation of lithium ions: during charging, lithium ions are deintercalated from the positive electrode, inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; during discharge, the opposite is true. Lithium-ion batteries actually use the concentration difference of lithium ions for energy storage and discharge. The absence of metal lithium or a composite containing metal lithium in the battery is the fundamental feature of lithium-ion batteries. The lithium metal battery is an energy storage system that directly uses elemental lithium (also known as metal lithium) as the negative electrode. The charging and discharging process of the lithium metal battery is essentially different from that of the lithium ion battery. The difference lies in the negative electrode side during the charging and discharging process. The form of energy conversion: during charging, lithium ions combine with electrons at the metal lithium negative electrode-electrolyte interface to deposit as metal lithium element, and when discharging, the opposite is true. The energy conversion form on the negative electrode side is essentially based on the deposition and stripping of metal lithium. Because there is no material such as carbon or silicon as a storage carrier for lithium ion intercalation, the mass of the negative side of the battery is reduced, making it have a very high mass energy density (mass energy density is the ratio of battery energy to battery mass).

It needs to be specified that the lithium batteries (or lithium secondary batteries and lithium-based batteries, etc.) that are widely used and talked about in daily life are all lithium-ion batteries, which are mentioned in the existing published patents. The protected lithium battery also refers to the lithium ion battery without additional instructions (that is, the appearance of the words such as metal lithium negative electrode, lithium metal battery or Lithium metal anode).

The reason why lithium metal batteries were abandoned in the last century is that lithium dendrites are easily formed during the charging process. After the lithium dendrites grow to a certain extent, they break into dead lithium, reducing the utilization rate of active lithium; the production of dead lithium will also Increase the internal resistance of the battery, resulting in a decrease in battery capacity; lithium dendrites continue to grow, and even pierce the separator, resulting in a short circuit between the positive and negative electrodes, resulting in thermal runaway. The charging method described in the present invention specifically refers to a method for charging the battery when the value of the state of charge (SOC, state of charge) of the battery is low. SOC refers to the ratio of the remaining capacity of the battery to the capacity of the fully charged state after a period of use or long-term shelving. It is usually expressed as a percentage, and its value ranges from 0 to 100%. When SOC=0, it means that the battery is fully discharged. When SOC=100%, the battery is fully charged. In different applications, the requirements for a lower SOC value are different. Usually, it is considered that the SOC is less than 50%, indicating that the value is lower and the battery needs to be charged. The charging process is for the purpose of the battery. Cycle use, and the process requires fast charging under high current conditions. For example, the US Department of Energy (DOE) issued a fast charging target in 2016 to charge the battery to a SOC greater than or equal to 80% within 15 minutes, and the fast charging process requires a high current of 10 mA cm ^-2 (Chang T , Kim H , Zutter BT , et al. Contents: (Adv. Funct. Mater. 30/2020) [J]. Advanced Functional Materials, 2020, 30(30).).

The rapid charging process of lithium metal batteries corresponds to the rapid deposition process of lithium ions at the negative electrode, which is a competitive process between the lithium ion deposition rate and the solution lithium supply rate at the interface. Studies have shown (Xiao J . How lithiumdendrites form in liquid batteries[J]. Science, 2019, 366(6464):426-427.) that the growth of lithium dendrites originates from the slow diffusion and charge of lithium ions in the electrolyte. Lithium ion concentration gradient formed by the migration rate. Under high current charging conditions (corresponding to the rapid deposition of lithium metal), lithium ions are rapidly consumed at the negative electrode interface, resulting in a lithium ion dissipation layer, and metallic lithium tends to grow vertically to the electrode and enter the electrolyte liquid phase to capture the lithium required for deposition. ions, resulting in lithium dendrites. Therefore, how to slow down the dissipation of Li ions at the anode interface is the key to stable Li deposition during fast charging.

With the advancement of material science and characterization technology in recent decades, overcoming the core problems of lithium metal batteries and rearranging their commercial market has become the focus of companies including CATL, Tesla, SAIC and other companies. Some scientific papers (for example, Zhang C, Wu B, Zhou Y, et al. Mussel-inspired hydrogels: from design principles to promising applications [J]. Chemical Society Reviews, 2020, 49.) and patents provide stable lithium metal deposition Strategy: For example, using a three-dimensional conductive matrix or a foam matrix as the lithium deposition framework (CN110518254B, CN110010895B), by reducing the local current density to homogenize the lithium ion flow, to achieve stable deposition of lithium metal under high current conditions, however, non- The introduction of an active skeleton will increase the quality of the system and reduce the energy density of the battery. When the lithium deposition fills the skeleton, the skeleton cannot perform its function, and the problem of lithium dendrites still occurs. For another example, a high-concentration salt electrolyte that can form a stable solid electrolyte interface film (SEI) is used to stabilize lithium metal deposition (CN110890592B, CN111276744A), but the use of high-concentration salt doubles the cost of electrolyte preparation, which is difficult to increase. scale application. The development of simple, economical, and efficient methods to achieve stable deposition of lithium metal under fast charging remains a century-old problem plaguing both academia and industry.

The change of the charging method can reduce the battery charging time and stabilize the battery cycle. However, the existing disclosed charging technologies are basically based on the CC-CV charging method (constant current-constant voltage) of lithium-ion batteries. It is based on the lithium-ion battery charging protocol (Ouyang M. eTransportation[J].eTransportation, 2019, 1:100013.; Hussein AH, Batarseh I. A Review of Charging Algorithms for Nickel and Lithium Battery Chargers[J]. IEEETransactions on Vehicular Technology, 2011, 60(3):830-838.), that is, the initial constant current charging to the cut-off voltage (CC stage), and then the constant voltage charging to a small current close to 0 (CV stage). Since there are differences in the area size of different batteries, and the current density describes the current size per unit area, using the current density to describe the electrical signal response when the battery is charging can avoid the interference of the battery size and make the description more scientific. Therefore, the present invention The charging current without special description in the description refers to the charging current density, and the unit is mA·cm ^-2 . In the constant voltage charging (CV) stage, the battery is charged at a constant voltage. At this time, the charging current generally shows a process of gradually decreasing or first increasing and then decreasing. The highest value that the charging current density can reach is the peak charging current density. , which can be detected and recorded by the current detection unit of the charging device. A specific current value can be set as the cut-off condition for constant voltage charging through the charging device. Constant current charging refers to the operation of charging the battery with a constant current. The charging current density is constant. At this time, the voltage of the battery being charged shows a gradually rising trend. A specific voltage value can be set by the battery charging device as the constant current charging Deadline. The late constant voltage process (CV stage) can make the lithium ion concentration distribution in the positive and negative electrode intercalation materials of lithium ion batteries more uniform, which is very important for the positive electrode material to exert a high specific capacity. The simple operability of this CC-CV charging method makes it the most widely used standard charging protocol. Many studies have proposed that adjusting the current during the charging process can slow down the aging of the battery and reduce the charging time. The purpose of these studies is often to reduce heat generation, avoid lithium precipitation or reduce mechanical stress, and thus generate MCC-CV based on CC-CV. CV method: It consists of two or more steps of constant current phase followed by a constant voltage phase. The MCC-CV method is essentially a coupled charging method of the initial constant current and the subsequent constant voltage, so it is also classified into the CC-CV method. In addition, the improved lithium-ion battery charging method also includes CP-CV method (constant power-constant voltage charging), PulseCharging (pulse current charging) method, BoostingCharging (enhanced charging, namely CC-CV-CC-CV) method and variable current charging methods, etc. (see Figure 1).

At present, there are very few charging technologies specially developed for lithium metal batteries. The charging method of lithium metal batteries refers to the CC-CV method of lithium ion batteries and related improvement methods. In the limited research of lithium metal battery charging technology, such as US patent US2018/0026464Al, the inventor proposed a new charging method, namely CC ₁ -CC ₂ -CV charging method. This patent uses a relatively large first constant current CC ₁ for short charging, in order to form a layer of initially uniform and stable lithium metal nuclei to facilitate the stable growth of lithium nuclei, thereby suppressing the generation of lithium dendrites. (Li Z , Wang ZL . Special Issue: Research Highlights in the Beijing Institute of Nanoenergy and Nanosystems (Adv. Funct. Mater. 41/2019) [J]. Advanced Functional Materials, 2019, 29(41).) coincidentally. It can be seen from the above that this charging method is essentially the MCC-CV method of initial constant current charging (see (b) in Figure 1), which is also classified as the CC-CV method. In fact, the initial high current is indeed conducive to the formation of lithium metal nuclei (Pei A, Zheng G, Shi F, et al. Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal [J]. Nano Letters, 2017, 17(2):1132.) , which also means faster charging speed, but continuous high current charging will inevitably lead to rapid consumption of lithium ions at the negative electrode interface, resulting in a lithium ion dissipative layer and inducing lithium dendrite growth (Xiao J . How lithium dendritesform in liquid batteries [J]. Science, 2019, 366(6464):426-427.), and the optimal duration of the initial constant current is difficult to define. If the duration is not long enough, it will not be able to form abundant crystal nuclei. If the time is too long, it will easily lead to the growth of lithium dendrites and short circuit of the battery.

It is not difficult to find that among the simple or complex charging methods favored by lithium-ion batteries, constant current charging (with a first constant current period) is used in the initial charging stage, and the difference is nothing more than the adjustment of the initial current or current step. The initial constant voltage charging (with a first constant voltage period) is absolutely rejected for two reasons: First, the operating voltage of commercial lithium-ion batteries is usually greater than 3.4V, that is, when the applied voltage needs to be at least 3.4V or more to charge the battery effectively. If charged with an initial constant voltage, this larger voltage would result in positive electrode materials such as lithium cobalt oxide (3.9V, layered structure), nickel-cobalt-manganese ternary (3.8V, layered structure) and lithium iron phosphate (3.4V , polyanionic structure) and other structures collapse or even powder (Masashi Okubo,SeongjaeKo, DebasmitaDwibedi. Designing positive electrodes with high energydensity for lithium-ion batteries[J]. Journal of Materials Chemistry A, 2021,9:7407-7421. ), resulting in a rapid decline in battery capacity and a significant reduction in battery life. Second, in the process of charging lithium-ion batteries, if the initial constant voltage charging is used, the initial charging current will be huge. Although a large current means that the charging speed is accelerated, the polarization effect generated by the initial huge current will cause the negative side potential to continuously decrease. , and eventually drops below 0V, resulting in lithium precipitation on the surface of the negative electrode, affecting the service life and even causing potential safety hazards (Trini, M; Jørgensen, Hauch P, et al.Journal of The Electrochemical Society - Research outputs - Research -Journal articles - DTU Orbit (09/03/2019).).

In view of the essential difference in the energy storage mechanism between lithium ion batteries and lithium metal batteries explained in the background art, the charging method designed based on the core problems of lithium ion batteries cannot be directly transplanted into lithium metal batteries to take effect, even constant voltage and lithium metal batteries. The effect of constant current, the two most fundamental charging building blocks, on Li metal deposition is also unknown. The inventors found that lithium metal batteries running with the standard charging protocol CC-CV are prone to short-circuit lithium dendrites under fast charging conditions, and their lifespan is short. Therefore, it is necessary to systematically explore the two most basic charging methods, constant voltage and constant current. The influence of structural units on lithium metal deposition and the invention of new fast charging methods specifically applicable to lithium metal batteries to suppress the generation of lithium dendrites are very important for the development of high-energy fast-charging battery systems.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the inventor proposes a new charging method, which is a coupled charging method of the first constant voltage (CV ₁ ) charging and the subsequent constant current-constant voltage (CC-CV ₂ ) charging . During the research process, the inventor unexpectedly found that the charging method broke the traditional academic thinking, and initially charged with a constant voltage. This charging method can reduce the lithium ion dissipation layer at the negative electrode interface and make the lithium metal deposited densely and smoothly. , thereby inhibiting the growth of lithium dendrites, effectively protecting the lithium metal-based electrode, prolonging the service life, and improving the safety of fast charging.

The specific plans are as follows:

The present invention provides a charging method for a lithium metal battery. The charging method is a coupled charging method of a first constant voltage (CV ₁ ) charging and a subsequent constant current-constant voltage (CC-CV ₂ ) charge, namely CV ₁ -CC- CV ₂ charging method, the charging method includes the following steps:

1) Obtain the actual working voltage and rated power of the lithium metal battery to be charged, wherein the value of the actual working voltage provides a reference for the value of the first constant voltage (CV ₁ ), and the value of the first constant voltage (CV ₁ ) It needs to be no less than the actual working voltage of the battery + 0.2V, and can not exceed the actual working voltage of the battery + 1V. For example, if the working voltage of the lithium metal/single sulfur battery is 2.1V, the value of the applied CV ₁ is 2.3V ≤CV ₁ ≤3.1V; the value of the rated power is used to calculate the state of charge (SOC) of the lithium metal battery to be charged;

2) Start constant voltage charging, and the charging voltage is the first constant voltage (CV ₁ );

3) After starting the first constant voltage (CV ₁ ) charging, the charged power of the lithium metal battery to be charged is detected, and the ratio of the charged power to the rated power is the state of charge (SOC) of the battery, SOC=charged power/rated power;

4) Determine whether the battery continues constant voltage charging according to the SOC value, and stop the first constant voltage (CV ₁ ) charging when the SOC value exceeds a set value;

5) After stopping the first constant voltage (CV ₁ ) charging, switch to constant current (CC) charging;

6) After starting constant current (CC) charging, detect the voltage or charged power of the lithium metal battery to be charged, and stop the constant current (CC) charging when the voltage rises to the set voltage value or the SOC exceeds the set value ;

7) After stopping constant current (CC) charging, switch to the second constant voltage (CV ₂ ) charging;

8) Detect the charging current of the lithium metal battery to be charged after starting the second constant voltage (CV ₂ ) charging, and stop the second constant voltage (CV ₂ ) charging when the current drops to the set current value, charging completed;

The values of the first constant voltage (CV ₁ ) and the second constant voltage (CV ₂ ) are equal or different.

Using the traditional standard charging protocol (CC-CV stage), when the lithium metal battery is rapidly charged, the lithium ions on the electrolyte-lithium metal negative electrode interface will be rapidly consumed, so the negative electrode needs to capture lithium ions into the electrolyte liquid phase during charging, resulting in Li metal deposition at the tip, and even growth of lithium dendrites to pierce the separator, cause safety accidents. If the first stage of the charging protocol is only high-current charging (that is, the standard charging protocol CC-CV), the deposition morphology of the negative electrode side is thin and sharp lithium dendrites, resulting in low utilization of active lithium (low Coulomb efficiency on the lithium side), The electrode polarization is severe and the capacity decays, and even the continuous growth of lithium dendrites eventually pierces the separator and causes the battery to short-circuit.

The inventor unexpectedly found that the introduction of the initial constant voltage stage before the standard charging protocol (CC-CV stage) can strengthen the internal electric field of the battery, promote the migration of lithium ions in the electrolyte to the negative electrode, and slow down the rapid consumption of lithium ions at the interface during fast charging. Compared with the traditional charging method (CC-CV), this method can make the lithium deposition dense and flat, inhibit the growth of lithium dendrites, prolong the service life, and improve the safety of fast charging.

Among them, the first constant voltage can also be called the first constant voltage, denoted as CV ₁ ; the second constant voltage can also be called the second constant voltage, denoted as CV ₂ ; the constant current can also be called the constant current, denoted as CC .

Preferably, in step 4), the set value of the state of charge of the battery is 5% to 100%, and when the state of charge of the battery is 100%, it corresponds to the whole process of constant voltage charging. The method for the whole process of constant voltage charging is as follows:

1) Obtain the actual working voltage and rated power of the lithium metal battery to be charged;

2) Start constant voltage charging with the first constant voltage (CV ₁ );

3) Detecting the charged power and charging current of the lithium metal battery to be charged, and the ratio of the charged power to the rated power is the state of charge (SOC) of the battery;

4) When the value of the state of charge (SOC) of the battery reaches 100%, the constant voltage charging is stopped, and the charging is completed; or when the current drops to the set current value, the constant voltage charging is stopped, and the charging is completed.

In the constant voltage charging stage, including the first constant voltage CV ₁ and the second constant voltage CV ₂ , the set current value refers to the value at which the current reaches a very small level, usually the set current value is 0.1C or less. It may be 0.05C or less, or 0.01C or less. Among them, C is used to represent the battery charge and discharge capacity rate. 1C represents the amperage when the battery is fully discharged in one hour. For example, a 18650 battery with a nominal name of 2200mA·h is discharged for 1 hour at 1C intensity, and the discharge current is 2200mA at this time.

Preferably, the values of the first constant voltage and the second constant voltage are between 1V and 3.5V.

Preferably, the values of the first constant voltage and the second constant voltage are between 1.5V and 3.2V.

Preferably, the value of the constant voltage is related to the type of the assembled battery, and the value of the constant voltage needs to be no less than the working voltage of the battery + 0.2V, and cannot exceed the working voltage of the battery + 1V. When the working voltage is 2.1V, the value of the applied CV ₁ is 2.3V≤CV ₁ ≤3.1V.

Preferably, the peak value of the current density corresponding to the charging stage of the first constant voltage (CV ₁ ) is not less than 10 mA·cm ⁻² .

Preferably, the constant current is a single constant current, and the current density of the single constant current is 0.01-10 mA·cm ⁻² .

Preferably, the constant current is a step constant current, the step constant current includes at least two current plateaus, and the current density of each current plateau is 0.01-10 mA·cm ⁻² .

More preferably, the current density of each current platform is 0.5-5 mA·cm ⁻² .

Preferably, the negative electrode material of the lithium metal battery is metal lithium or a composite containing metal lithium. Further, the composite containing metallic lithium is selected from lithium metal alloys or lithium metal-carbon materials.

The lithium metal alloy is selected from any one of lithium aluminum alloys, lithium magnesium alloys, lithium tin alloys, lithium boron alloys, and lithium indium alloys.

The carbon material is selected from any one of graphite, graphene, carbon nanotubes, and carbon nanowires.

Preferably, the positive electrode of the lithium metal battery is a low-operating voltage positive electrode material, and the voltage of the low-operating voltage positive electrode material needs to be less than or equal to 3V (vs Li ⁺ /Li). Among them, the voltage has no absolute value, and a reference object is required. All potentials in the present invention are not otherwise specified, and are based on the potential of the lithium metal electrode as a reference, that is, vs Li+/Li.

Preferably, the low working voltage positive electrode material is selected from any one of lithium titanate, organic lithium storage material, elemental sulfur or oxygen.

Preferably, the organic lithium storage material is selected from organic sulfides or oxygen-containing conjugated organics.

Preferably, pure lithium metal is selected as the negative electrode material, and elemental sulfur is selected as the positive electrode material.

It should be pointed out that, for lithium metal batteries, if the negative electrode material is metal lithium or a composite containing metal lithium, the potential of the negative electrode has also been determined, then the working voltage of the battery depends on the type of positive electrode material (electrode potential). Depending on the properties of the material itself, it can be obtained by the Nernst equation or quantum chemical calculation), or the voltmeter can be used to analyze the battery during the charging process, and the actual working voltage can be obtained by detection and calculation. Since the negative electrode material of lithium ion battery uses graphite or silicon without lithium source, the positive electrode material of lithium ion battery must contain lithium source for energy conversion, and its positive electrode material is limited to lithium cobalt oxide (3.9V, layered structure) , nickel-cobalt-manganese ternary (3.8V, layered structure) and lithium iron phosphate (3.4V, polyanionic structure), etc. (Yang L , Yang K , Zheng J , et al. Harnessing the surfacestructure to enable high-performance cathode materials for lithium-ionbatteries[J]. Chemical Society Reviews, 2020, 49.). In contrast, for a lithium metal battery using lithium metal as the negative electrode, since there is a lithium source on the negative electrode side, in addition to the above-mentioned lithium-containing positive electrode material, a positive electrode material that does not contain a lithium source can also be used as the positive electrode material, such as elemental material. Sulfur, oxygen, organic lithium storage materials, etc. Li-metal batteries composed of organic lithium storage materials (1.9 V), elemental sulfur (2.1 V) or oxygen (2.8 V) positive electrodes and lithium metal negative electrodes have low operating voltages. The low operating voltage means that even with constant voltage charging, the voltage value used is small and does not cause significant structural damage to the cathode material; on the other hand, these low-voltage materials are not harshly layered or For crystalline substances such as olivine structures, there is no need to worry about voltage damage to their structures.

The lithium metal battery of the present invention uses the above-mentioned positive electrode material and negative electrode material as positive and negative electrodes respectively, and is assembled together with a suitable electrolyte and a separator. Specifically, the constant voltage and constant current basic modules are respectively connected to the assembled lithium metal battery and charged. As the fast charging method of the lithium metal battery of the present invention, the charging method is a coupling method of initial constant voltage (CV) charging and subsequent constant current-constant voltage (CC-CV) charging, namely CV ₁ -CC-CV ₂ charging method . The initial constant voltage is the first constant voltage, denoted as CV ₁ , and the constant voltage in the subsequent CC-CV stage is the second constant voltage, denoted as CV ₂ . Specifically, the constant voltage and constant current basic modules are respectively connected to the assembled lithium metal battery and charged.

As a preference of a fast charging method for the lithium metal battery of the present invention, the value of the charging voltage CV ₁ is 1V≤CV ₁ ≤3.5V, and the constant voltage charging cut-off condition is that the SOC reaches 20%≤SOC≤100%. SOC (State of charge), the state of charge of the battery, is used to reflect the remaining capacity of the battery, and its value is defined as the ratio of the remaining capacity to the battery capacity, expressed as a percentage. Its value ranges from 0 to 1. When SOC=0, it means that the battery is fully discharged, and when SOC=1, it means that the battery is fully charged. Preferably, the value of the charging voltage CV ₁ is 1.5V≦CV ₁ ≦3.2V.

Further preferably, the value of the constant current CC is 0.2C≤CC≤3C, and the constant current charging cut-off condition is that the voltage is greater than or equal to 2.6V. Among them, C is used to represent the battery charge and discharge capacity rate. 1C represents the amperage when the battery is fully discharged in one hour. For example, a 18650 battery with a nominal name of 2200mA·h is discharged for 1 hour at 1C intensity, and the discharge current is 2200mA at this time.

Further preferably, the value of the second constant voltage CV ₂ is between 1V and 3.5V; preferably, the value of the second constant voltage CV ₂ is between 1.5V and 3.2V.

Further preferably, the charging voltage CV ₂ is 2.6V, and the constant voltage charging cut-off condition is that the current is less than 0.03C.

Through the experiment of the present invention, it is found that the use of CV ₁ -CC-CV ₂ charging, compared with the standard charging protocol CC-CV, can make the lithium metal deposition dense and smooth, inhibit the growth of lithium metal dendrites, and the assembled battery can be charged faster. Short, stable cycle and extended life.

The present invention also provides a charging device for a lithium metal battery, using the aforementioned charging method, comprising:

a power conversion unit that can provide constant current (CC) and constant voltage (CV ₁ or CV ₂ ) charging inputs;

a charge control switch and a discharge control switch, the charge control switch and the discharge control switch are connected in series with the power conversion unit to adjust the charge and discharge on-off;

A detection unit, the detection unit includes a voltage detection unit, a current detection unit and a power detection unit, the voltage detection unit is used to detect the voltage at both ends of the battery, and the current detection unit is used to detect the magnitude of the current passing through the battery, so The electric quantity detection unit is used for integrating current and time to obtain electric quantity;

a control circuit, the control circuit controls the output of the power conversion unit, including a voltage-current conversion unit (CV ₁ converted to CC) and a current-voltage conversion unit (CC converted to CV ₂ );

Human-machine interface interaction module, used to set specific input values and cut-off conditions for each stage of charging and discharging.

The values of CV ₁ (the first constant voltage) and CV ₂ (the second constant voltage) are equal or different.

Specifically, the operator first performs a charging test based on the CC-CV ₂ method on the charged battery through the man-machine interface interaction module, and the constant current CC and the constant voltage CV ₂ are provided by the power conversion unit. After the first cycle of charging is completed, the voltage detection unit will average the voltage during the battery charging process to obtain the actual working voltage of the battery; the power detection unit integrates the charging current and time to obtain the battery's full state of charge, that is, the battery rated power.

Start the CV ₁ -CC-CV ₂ charging operation, the operator inputs the specific input values and cut-off conditions of each stage of charging and discharging through the man-machine interface interaction module, the power conversion unit provides the charging input of the first constant voltage CV ₁ , and the current detection unit The charging current at this stage is detected in real time, and the current and time are integrated and converted in real time. The integration result is the charged power, and the ratio of the charged power to the rated battery power is the SOC, which is also calculated and updated by the detection unit in real time. When the SOC value exceeds the set value, the first constant voltage (CV ₁ ) charging is stopped by the charging control switch, and constant current (CC) charging is performed by the power conversion unit.

The voltage detection unit will detect the voltage during the charging process of the battery in the CC phase to obtain the real-time battery voltage. When the real-time voltage rises to the set voltage value, the constant current (CC) charging will be stopped; or, when the real-time updated SOC value The constant current (CC) charging can also be stopped when the set value is exceeded. The constant current (CC) charging is stopped by the charging control switch, and the second constant voltage (CV ₂ ) charging is performed by the power conversion unit.

The charging current in the second constant voltage (CV ₂ ) stage is detected by the current detection unit, and when the current drops to the set current value, the constant current (CC) charging is stopped, and the charging is completed.

According to the charging device, a coupling method of the initial constant voltage (CV) charging and the subsequent constant current-constant voltage (CC-CV) charging of the lithium metal battery, ie, the CV ₁ -CC-CV ₂ charging method, can be realized.

It should be pointed out that, compared with the existing charging technology based on lithium-ion battery design, the present invention proposes to add an initial constant voltage charging process on the basis of the standard charging protocol CC-CV, that is, to propose CV ₁ -CC-CV ₂ charging methods. The initial constant voltage stage was discarded because it was harmful to commercial lithium ion batteries, but in the present invention, it was unexpectedly found that this process greatly improved the fast charging performance of lithium metal batteries.

The beneficial effect of the CV ₁ -CC-CV ₂ method proposed by the present invention is that: in the initial constant voltage stage, CV ₁ can generate a charging current that gradually decreases from high to high ((f) in FIG. 1 ), which is beneficial to the rapid nucleation of lithium metal, And the gradually decreasing current reduces the risk of lithium dendrite generation compared to direct initial high-current charging. In addition, the constant voltage will strengthen the electric field in the battery and promote the migration of lithium ions to the negative electrode with low potential, which can slow down the dissipation of lithium ions at the negative electrode interface, and further make the deposited lithium metal morphology flat and dense. The method effectively inhibits the growth of lithium dendrites, thereby protecting the lithium metal electrode simply, conveniently and efficiently, prolonging the life of the electrode, and improving the cycle stability and safety.

Description of drawings

Figure 1 is a schematic diagram of the voltage and current changing with time in various charging methods. The horizontal axis represents the charging time, and the vertical axis represents both the charging voltage (solid line) and the corresponding charging current (dotted line). (a) for standard constant current-constant voltage (CC-CV) charging, (b) for step current-constant voltage (MCC-CV) charging in Fig. 1, (c) for constant power-constant voltage in Fig. 1 Voltage (CP-CV) charging, (d) in Figure 1 is Pulse Charging, (e) in Figure 1 is Boosting Charging, (f) in Figure 1 is proposed by the present invention Constant voltage-constant current-constant voltage (CV ₁ -CC-CV ₂ ) charging method;

Fig. 2 is the coulombic efficiency comparison diagram of the lithium copper batteries prepared in Example 1 and Comparative Example 1 under constant current and constant voltage deposition conditions;

3 is a graph of the charge-discharge current curve of the lithium-copper battery prepared in Example 1 under constant voltage deposition conditions;

Fig. 4 is the SEM photo of lithium metal deposition under the constant current deposition condition adopted in Comparative Example 1 (left image), and the SEM photo of lithium under the constant voltage deposition condition in Example 1 (right image) ;

Figure 5 is a comparison diagram of the characteristic capacity and charging time of the prepared lithium-lithium titanate battery under CC-CV (Comparative Example 2) and CV ₁ -CC-CV ₂ (Example 2) fast charging conditions;

Fig. 6 is the charge-discharge current curve diagram of the lithium-lithium titanate battery prepared in Example 2 under the CV ₁ -CC-CV ₂ charging condition;

Fig. 7 is the characteristic capacity comparison diagram of the prepared lithium-sulfur battery under the conditions of CC-CV (Comparative Example 3) and CV ₁ -CC-CV ₂ (Example 3);

8 is a comparison chart of the normalized characteristic capacity of the lithium-sulfur battery prepared from the control group in Example 5 under the conditions of the CC-CV stage and the CV ₁ -CC-CV ₂ stage.

Detailed ways

In order to make the invention purpose, technical solution and technical effect of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments given in this specification are only for explaining the present invention, not for limiting the present invention, and the present invention is not limited to the embodiments given in the specification.

Specifically, the present invention relates to a fast charging method and a charging device based on a lithium metal battery. The negative electrode material of the lithium metal battery is metal lithium or a composite containing metal lithium. Further, the composite containing metallic lithium is selected from lithium metal alloys or lithium metal-carbon materials. The lithium metal alloy is selected from any one of lithium aluminum alloys, lithium magnesium alloys, lithium tin alloys, lithium boron alloys, and lithium indium alloys. The carbon material is selected from any one of graphite, graphene, carbon nanotubes, and carbon nanowires. It is fundamentally different from commercial lithium-ion batteries using graphite-based or silicon-based negative electrodes in terms of energy conversion principles and performance constraints. The cathode of the lithium metal battery is a cathode material with low working voltage (≤3V vs Li ⁺ /Li), such as lithium titanate (1.5V), organic lithium storage material (1.9 V), elemental sulfur (2.1V) or oxygen ( 2.8V), etc., and use high working voltage materials such as lithium iron phosphate (3.4V), nickel cobalt manganese ternary material (3.8 V), lithium cobalt oxide (3.9 V) or lithium manganate (4.0 V) as the positive electrode. Lithium-ion batteries are different. The charging method is a coupling method of initial constant voltage (CV) charging and subsequent constant current-constant voltage (CC-CV) charging, that is, a CV ₁ -CC-CV ₂ charging method. Specifically, the charging method first determines the actual working voltage of the lithium metal battery to be charged (the voltage is determined by the type of positive electrode material); and then applies a first constant voltage (CV ₁ ) that is at least 0.2V greater than the working voltage for charging, The charging cut-off condition at this stage is to reach at least 5% of the battery state of charge (SOC); then coupled with a common standard charging protocol (CC-CV) for conventional charging, the CV in the conventional charging is the second constant voltage (CV ₂ ), the values of CV ₁ and CV ₂ can be equal or unequal. When the lithium metal battery is rapidly charged, the lithium ions on the electrolyte-lithium metal negative electrode interface will be rapidly consumed, so the negative electrode needs to capture lithium ions in the electrolyte liquid phase during charging, resulting in the deposition of sharp lithium metal, and even the growth of lithium dendrites and thorns. Wearing the diaphragm causes a safety accident. If the first stage of the charging protocol is only high-current charging (that is, the standard charging protocol CC-CV), the deposition morphology of the negative electrode side is thin and sharp lithium dendrites, resulting in low utilization of active lithium (low Coulomb efficiency on the lithium side), The electrode polarization is severe and the capacity decays, and even the continuous growth of lithium dendrites eventually pierces the separator and causes the battery to short-circuit. The charging method proposed by the present invention adopts constant voltage (first constant voltage) charging in the initial stage, which is essentially different from the initial constant current (first constant current) charging in the standard charging method. By using the charging method of the present invention, an initial constant voltage stage (which has a negative impact on traditional lithium ion batteries and is not adopted) is introduced before the standard charging protocol, which can strengthen the internal electric field of the battery and promote the migration of lithium ions in the electrolyte to the negative electrode. Slow down the rapid consumption of lithium ions at the interface during fast charging. Compared with the traditional charging method (CC-CV), this method can make the lithium deposition dense and smooth, inhibit the growth of lithium dendrites, prolong the service life, and improve the safety of fast charging. .

Comparative Example 1

Since lithium metal batteries are different from lithium ion batteries, the influence of the two most basic charging structural units, constant voltage and constant current, on the lithium metal negative electrode is discussed. Therefore, the same lithium-copper battery was first assembled in Comparative Example 1 and Example 1. The charging corresponds to the process of depositing lithium ions in the electrolyte to form lithium metal on the copper current collector. The electrodes on both sides will be covered with active lithium metal, which can be excluded. Interference of other active species to demonstrate the effect of constant voltage or constant current charging cells on lithium metal electrodes. Since lithium is deposited on copper, the electrodes on both sides are lithium metal, so its actual working voltage is 0, and it does not have the function of energy storage. The lithium-copper battery systems in Comparative Example 1 and Example 1 are mechanistic research tools, which are only used to eliminate the interference of the positive electrode, and focus on the study of the effect of constant voltage or constant current charging on the lithium metal electrode.

The negative metal lithium and the positive copper sheet were assembled into a lithium copper battery, and the electrolyte was 1MLiTFSI/DOL-DME/2%LiNO ₃ .

The charge-discharge cycle test was carried out by connecting a constant current under the following conditions: the deposition current density was 12 mA·cm ^-2 , the deposition power was 1 mAh·cm ^-2 , and the deposition time was 5 min; the stripping current was 1 mA·cm ^-2 . The deposition current density, deposition power, and deposition time are charging current density, charging power, and charging time. The deposited electricity is 1 mAh·cm ⁻² , which is the rated electricity in Example 1.

After the charge-discharge cycle test, the coulombic efficiency of the lithium-copper battery dropped rapidly and was less than 40% after 30 cycles.

Example 1

Assemble the same battery as in Comparative Example 1: Assemble the negative metal lithium and the positive copper sheet into a lithium copper battery, and the electrolyte is 1M LiTFSI/DOL-DME/2% LiNO ₃ .

The actual working voltage of the lithium-copper battery is detected and calculated by the charging device, which is 0V, and the rated power is 1mAh·cm ^-2 .

Example 1 is the whole process of constant voltage charging, and the deposition process adopts constant voltage under the following conditions: the deposition voltage is 0.25V, the deposition power is 1mAh·cm ^-2 , the average deposition time is less than 5min, and the stripping current is 1mA·cm ^-2 . The deposition power and the deposition time are the charging power and the charging time.

Constant voltage deposition is constant voltage charging, corresponding to CV ₁ in the CV ₁ -CC-CV ₂ method, the value of CV ₁ is the actual working voltage of the battery + 0.25V, that is, CV ₁ is 0.25V; and the condition for the end of the CV ₁ stage When the SOC reaches 100%, it corresponds to the whole process of constant voltage charging.

After the charge-discharge cycle test, the lithium metal battery was charged at a constant voltage using the conditions in this example, the charging peak current was greater than 16 mA·cm ^-2 , the cycle was at least 40 cycles, and the coulombic efficiency remained above 90%.

Figure 2 shows the comparison of coulombic efficiencies of lithium-copper batteries under constant current and constant voltage deposition of lithium. Figure 3 shows the corresponding current diagrams under constant voltage charge and discharge conditions. FIG. 4 shows the SEM photographs of metallic lithium under the constant voltage deposition conditions of Comparative Example 1 and Example 1, respectively. It can be found from the observation that during the constant voltage deposition process in Example 1, the surface of the lithium metal electrode is denser and smoother than that under constant current conditions, and tends to grow in a plane, which inhibits the generation of lithium dendrites.

Comparative Example 2

A lithium metal-based battery (lithium-lithium titanate battery) was assembled with a 45μm-thick thin metal lithium sheet as the negative electrode and the positive electrode lithium titanate electrode, and the electrolyte was 1MLiTFSI/DOL-DME/2%LiNO ₃ .

Carry out the charge-discharge cycle test according to the CC-CV protocol of the prior art, the conditions are as follows: constant current charging, the charging current rate is 6C (1C is about 0.935mA·cm ^-2 ), when the voltage reaches 3V, it is changed to 3V constant voltage charging , the cut-off condition of the constant voltage stage is that the current is less than 0.03C; the discharge rate is 2C, and the charge-discharge range is 1-3V (vsLi ⁺ /Li). Since the batteries of Comparative Example 2 and Example 2 are the same two batteries, they have the same actual working voltage and rated power. The charging device performs CC-CV charging on the battery of Comparative Example 2 (that is, charging by the CC-CV ₂ method), and the voltage detection unit averages the first-round charging voltage of the battery in Comparative Example 2, so as to obtain the battery The actual working voltage of the battery; the power detection unit integrates and converts the charging current and time of the first cycle of the battery in Comparative Example 2 to obtain the power of the battery in a fully charged state, that is, the rated power. After the charge-discharge cycle test, the lithium source of the negative electrode of the lithium-lithium titanate battery was rapidly consumed, and the capacity began to decrease rapidly after 40 cycles.

Example 2

Assemble the same battery as in Comparative Example 2: 45 μm thick thin metal lithium sheet is used as the negative electrode and the positive lithium titanate electrode is assembled into a lithium metal battery (lithium-lithium titanate battery), and the electrolyte is 1M LiTFSI/DOL-DME/2 % LiNO ₃ .

The actual working voltage of the lithium-lithium titanate battery is detected and calculated by the charging device, which is 1.55V (vs Li ⁺ /Li)), and the rated power is the rated power described in Comparative Example 2.

The CV ₁ -CC-CV ₂ protocol was used to charge, and the cycle test was carried out under the following conditions: constant voltage charging, the charging voltage CV ₁ is the actual working voltage of the battery +0.35V, which is 1.9 V (vs Li ⁺ /Li).

Example 2 is the whole process of constant voltage charging, and the charging cut-off condition is that the charging current density is less than the minimum value, that is, less than 0.03C, and then the single-turn charging stops and discharges; the discharge rate is 2C, and the discharge interval is 1 ~ 3V (vs Li ⁺ /Li).

After the charge-discharge cycle test, the lithium metal battery was charged at constant voltage using the conditions in this example, the peak current in the constant-voltage phase reached 27 mA·cm ^-2 , the battery was cycled for at least 100 cycles, the capacity remained stable, and the charging time was reduced to Half in Comparative Example 2, about 3 minutes.

FIG. 5 presents a comparison diagram of the characteristic capacity and charging time of the lithium-lithium titanate battery under the charging conditions of Comparative Example 2 and Example 2. In Example 2, the original CV ₁ -CC-CV ₂ charging method was used, and the capacity of the battery remained stable within 100 laps, while the battery in Comparative Example 2 using the CC-CV method began to decay significantly after 45 laps. In addition, considering the charging time, the charging time of the battery in the example is shortened to within a stable 3 minutes, while the charging time of the battery in the comparative example exceeds 6 minutes within 45 cycles of the stable cycle.

FIG. 6 shows the charge-discharge current curve diagram of the lithium-lithium titanate battery in the case of Example 2. Observing the graph, it can be found that during the charging process of CV ₁ -CC-CV ₂ , the peak charging current is as high as 27 mA·cm ^-2 , which can greatly shorten the charging time.

Comparative Example 3

A lithium metal battery was assembled with a 45 μm thick thin metal lithium sheet as the negative electrode and the positive sulfur electrode sheet, and the electrolyte was 1MLiTFSI/DOL-DME/2%LiNO ₃ .

The CC-CV protocol is used for the charge-discharge cycle test. The conditions are as follows: After the battery is stable in cycles (that is, the capacity remains stable, and the number of cycles is greater than 50 cycles), the charging current rate is converted from 0.2C to 1C (1C is about 3.33mA· cm ^-2 ), when the voltage reaches 2.6V, it is changed to 2.6V constant voltage charging. The cut-off condition of the constant voltage stage is that the current is less than 0.03C; ⁺ /Li). Since the batteries of Comparative Example 3 and Examples 3 and 4 are the same three batteries, they have the same actual working voltage and rated power. The charging device charges the battery of Comparative Example 3 by the CC-CV method, and the voltage detection unit averages the charging voltage of the first cycle of the battery in Comparative Example 3 to obtain the actual working voltage of the battery; the power detection unit compares the comparative example In 3, the charging current of the first lap of the battery and the time are integrated and converted to obtain the power of the battery in a fully charged state, that is, the rated power. After the charge-discharge cycle test, the lithium source of the negative electrode of the lithium-sulfur battery is rapidly consumed, and the capacity decreases gradually.

Example 3

Assemble the same battery as in Comparative Example 3: A lithium metal-based battery was assembled with a 45 μm thin metal lithium sheet as the negative electrode and the positive sulfur electrode sheet, and the electrolyte was 1M LiTFSI/DOL-DME/2% LiNO ₃ .

The actual working voltage of the lithium-sulfur battery was detected and calculated by the charging device, and it was 2.1V (vs Li ⁺ /Li)), and the rated power was the rated power described in Comparative Example 3.

The charging adopts the CV ₁ -CC-CV ₂ method, and the cycle test is carried out under the following conditions: constant voltage charging, the charging voltage CV ₁ is the actual working voltage of the battery +0.45V, which is 2.55 V (vs Li ⁺ /Li).

Example 3 is the whole process of constant voltage charging. The charging cut-off condition is that the charging current density is less than the minimum value, that is, less than 0.03C, and then the single-turn charging stops and discharges; the discharge stage is 0.2C constant current discharge, and the discharge interval is 1.8 ~ 2.6 V (vs Li ⁺ /Li).

After the charge-discharge cycle test, the lithium metal battery was charged at constant voltage using the conditions in this example, the capacity remained stable, the fast-charge life was at least 70 cycles, and the charging time was kept within 12 minutes.

Figure 7 presents the characteristic capacity comparison of Li-S batteries under CC-CV and CV ₁ -CC-CV ₂ charging. Observing the graph, it can be found that during the charging process of CV ₁ -CC-CV ₂ , the capacity hardly decays.

Example 4

The same battery as in Comparative Example 3 was assembled, and a 45 μm-thick thin metal lithium sheet was used as the negative electrode and the positive sulfur electrode sheet to assemble a lithium metal battery, and the electrolyte was 1M LiTFSI/DOL-DME/2% LiNO ₃ .

The actual working voltage of the lithium-sulfur battery was detected and calculated by the charging device, and it was 2.1V (vs Li ⁺ /Li)), and the rated power was the rated power described in Comparative Example 3.

The CV ₁ -CC-CV ₂ method is used for charging, and the cycle test is carried out. The test process is carried out on the LAND electrochemical test device. The conditions are as follows: constant voltage charging, the charging voltage CV ₁ is the actual working voltage of the battery + 0.7V, that is is 2.8 V (vs Li ⁺ /Li).

Example 4 is the whole process of constant voltage charging. The charging cut-off condition is that the charging current density is less than the minimum value, that is, less than 0.05C, and then the single-turn charging is stopped and discharging is performed; V(vs Li ⁺ /Li). After the charge-discharge cycle test, the lithium metal battery was charged with constant voltage using the conditions in this example, and the capacity remained stable.

Example 5

A lithium metal battery with a thickness of 45 µm was assembled as the negative electrode and the positive sulfur electrode, and the electrolyte was 1MLiTFSI/DOL-DME/2% LiNO ₃ .

Further increasing the voltage value in the initial constant voltage stage can increase the charging current and reduce the charging time. In Example 5, increasing the 2.55V of Example 3 to 2.6V can further reduce the charging time. Due to the larger current it causes, it is easy to cause a short circuit of the battery. At this time, it is necessary to reduce the SOC contributed by the initial CV ₁ in CV ₁ -CC-CV ₂ to avoid short circuit of the battery. This example will use a self-control method to illustrate the superiority of CV ₁ -CC-CV ₂ charging.

The CC-CV protocol is used for the charge-discharge cycle test. The conditions are as follows: the CC charging current rate is 0.5C, and when the voltage reaches 2.6V, it is changed to 2.6V constant voltage charging. The cut-off condition of the constant voltage stage is that the current is less than 0.03C; the discharge process is 0.2C constant current discharge, the charge and discharge range is 1.8 ~ 2.6V (vs Li ⁺ /Li). The actual working voltage of the lithium-sulfur battery is calculated and detected by the charging device, which is 2.1V (vs Li+/Li)), and the rated power is the first full charge during the CC-CV charging process.

The battery capacity is completely stable after 50 laps. After 60 laps, it is changed to the method of CV ₁ -CC-CV ₂ for charging. The conditions are as follows: constant voltage charging, the charging voltage CV ₁ is the actual working voltage of the battery +0.5V, that is is 2.6V (vs Li ⁺ /Li), after the SOC of the CV ₁ stage reaches 50%, the first constant voltage charging is stopped and switched to CC constant current charging, and the CC charging current rate is 0.5C; when the CC stage voltage reaches When it is 2.6V, stop the constant current charging and change to 2.6V second constant voltage charging; when the current of the second constant voltage charging CV ₂ stage is less than 0.03C, the single-turn charging is completed, and it is turned to discharge; the discharge process is 0.2C Constant current discharge, the charge and discharge range is 1.8 ~ 2.6V (vs Li ⁺ /Li). Repeat this process for cyclic charge and discharge.

Figure 8 presents the comparison of normalized characteristic capacities of Li-S batteries under CC-CV and CV ₁ -CC-CV ₂ charging. It can be seen from the figure that in the control experiment, after changing to the CV ₁ -CC-CV ₂ method (after 60 cycles), the charge and discharge capacity of the battery has been improved by nearly 40% in the CC-CV stage. The kinetic performance of the surface lithium metal anode is greatly improved.

Claims (9)

1. A method for charging a lithium metal battery, characterized in that said charging method is a first constant voltage charging and a subsequent constant current-constant voltage coupled charging method, i.e. CV ₁ -CC-CV ₂ A charging method, comprising the steps of:

1) Acquiring the actual working voltage and rated electric quantity of a lithium metal battery to be charged;

2) Starting constant voltage charging, wherein the charging voltage is a first constant voltage;

3) Detecting the charged electric quantity of the lithium metal battery to be charged after the first constant voltage charging is started, wherein the ratio of the charged electric quantity to the rated electric quantity is the charge state of the battery;

4) Determining whether the battery continues constant voltage charging according to the value of the state of charge of the battery, and stopping the first constant voltage charging when the value of the state of charge of the battery exceeds a set value;

5) After the first constant voltage charging is stopped, the constant voltage charging is converted into constant current charging;

6) Detecting the voltage or the charged electric quantity of the lithium metal battery to be charged after the constant current charging is started, and stopping the constant current charging when the voltage rises to a set voltage value or the charge state of the battery exceeds a set value;

7) After the constant current charging is stopped, the constant current charging is converted into second constant voltage charging;

8) Detecting the charging current of the lithium metal battery to be charged after starting second constant voltage charging, and stopping the second constant voltage charging after the current drops to a set current value, so that the charging is finished;

the values of the first constant voltage and the second constant voltage are equal or different;

the lithium metal battery is configured by adopting a low-working-voltage anode material, the low-working-voltage anode material means that the anode material has an electrode potential less than or equal to 3V relative to metal lithium, and the value of the first constant voltage is not less than +0.2V of the actual working voltage of the battery and cannot exceed +1V of the actual working voltage of the battery.

2. The charging method according to claim 1, wherein in step 4), the set value of the battery state of charge is 5% to 100%, and when the battery state of charge is 100%, the whole process of constant voltage charging corresponds to the whole process of constant voltage charging, and the method of the whole process of constant voltage charging is as follows:

1) Acquiring the actual working voltage and rated electric quantity of a lithium metal battery to be charged;

2) Starting constant voltage charging at a first constant voltage;

3) Detecting the charged electric quantity and the charging current of the lithium metal battery to be charged, wherein the ratio of the charged electric quantity to the rated electric quantity is the charge state of the battery;

4) When the value of the charge state of the battery reaches 100%, stopping the constant-voltage charging and finishing the charging; or stopping the constant-voltage charging after the current is reduced to a set current value, and finishing the charging.

3. The charging method according to claim 1, wherein the first constant voltage and the second constant voltage have a value between 1V and 3.5V.

4. The charging method according to claim 1, wherein a peak value of a current density corresponding to a charging phase of the first constant voltage is not less than 10mA · cm ^-2 。

5. The charging method according to claim 1, wherein the constant current is a single constant current having a current density of 0.01 to 10 mA-cm ^-2 。

6. The charging method according to claim 1, wherein the constant current is a stepped constant current comprising at least two current levels, and the current density of each current level is 0.01 to 10mA · cm ^-2 。

7. The charging method according to claim 1, wherein the negative electrode material of the lithium metal battery is elemental metal lithium or a composite containing elemental metal lithium.

8. The charging method according to claim 1, wherein the low-operating-voltage positive electrode material is selected from any one of lithium titanate, an organic lithium storage material, elemental sulfur, or oxygen.

9. A charging device for a lithium metal battery, characterized in that the charging method according to claim 1 is used, and the charging device comprises:

a power conversion unit that can provide a constant current and constant voltage charging input;

the charging control switch and the discharging control switch are connected with the power conversion unit in series and used for adjusting charging and discharging on-off;

the detection unit comprises a voltage detection unit, a current detection unit and an electric quantity detection unit, wherein the voltage detection unit is used for detecting the voltages at two ends of the battery, the current detection unit is used for detecting the magnitude of the current passing through the battery, and the electric quantity detection unit is used for integrating the current and the time to obtain the electric quantity;

a control circuit that controls an output of the power conversion unit, including a voltage-current conversion unit and a current-voltage conversion unit;

and the human-computer interface interaction module is used for setting specific input values and cutoff conditions of each charging and discharging stage.

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