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

Method and apparatus for charging lithium metal battery Download PDF

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CN114725549B
CN114725549B CN202210567244.2A CN202210567244A CN114725549B CN 114725549 B CN114725549 B CN 114725549B CN 202210567244 A CN202210567244 A CN 202210567244A CN 114725549 B CN114725549 B CN 114725549B
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charging
battery
lithium
current
voltage
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CN114725549A (en
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陆盈盈
王鑫阳
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Zhejiang University ZJU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
    • H02J7/0048—Detection of remaining charge capacity or state of charge [SOC]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007—Regulation of charging or discharging current or voltage
    • H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Power Engineering (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

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 for 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
The lithium ion battery has wide application in the fields of smart phones, notebook computers, electric automobiles and the like, but with the development of society, the existing commercial lithium ion battery is difficult to meet the increasing demand of people on ultra-long endurance and fast charging electronic products. The lithium metal has a valence of 3860 mAh g -1 Ultra-high theoretical specific capacity (graphite 372mAh g) -1 ) And the lowest oxidation-reduction potential (-3.04V relative to the standard hydrogen potential), the energy density of the battery can be greatly improved. Active lithium metal has rapid kinetic reaction characteristics and thus also has the potential for rapid charging applications. Based on this, adoptLithium metal batteries using metal-containing lithium foils as negative electrodes are receiving increasing attention again in the field of commercial batteries.
In fact, the commercialized application of the lithium metal battery is earlier than the existing lithium ion battery, the battery adopting the metal lithium as the negative electrode was firstly introduced by the Moli Energy company in canada in the last 80 th century, the battery is also called the global battery market by the Moli Energy company, the lithium metal battery is easy to cause explosion due to a large amount of dendrites generated in the using process, and continuous fire explosion accidents occur in the lithium metal battery in 1989, so that the battery is called the global battery market to be recalled for a large area in the global scope, and the company called the global battery market for a short time is called the NEC company in japan and finally purchased by the NEC company in japan. In 1991, the Nippon Sony company traded the priority, and graphite material was used as the negative electrode to avoid the application of metallic lithium in the negative electrode, thereby avoiding the generation of lithium dendrites. At this point, lithium ion batteries begin to rush all the way, and quickly throw other types of batteries behind. Through the development of the last 30 years, the energy density and the charging performance of the lithium ion battery are remarkably improved, and the development of the lithium ion battery also reaches the bottleneck stage.
Lithium batteries generally refer to batteries containing Lithium elements, including Lithium-ion batteries (Lithium-ion batteries) and Lithium metal batteries (Lithium metal batteries). Further, lithium batteries are also known as lithium secondary batteries, lithium-based batteries, and the like. Lithium metal batteries are essentially different from lithium ion batteries (Nature Nanotechnology, 2017, 12, 194) in that they are essentially different in negative electrodes. The material of the negative electrode of the lithium ion battery is carbon material (graphite, soft carbon, hard carbon and the like) or silicon material, and the lithium metal battery is fundamentally characterized in that the material of the negative electrode adopts a metal lithium simple substance or a compound containing the metal lithium simple substance. The cathode of the existing lithium ion battery is made of carbon materials (graphite, soft carbon, hard carbon and the like) or silicon materials, and a lithium-containing compound is used as a cathode material; the lithium metal battery takes a metal lithium simple substance or a compound containing the metal lithium simple substance as a negative electrode material, a positive electrode adopts a positive electrode material with low working voltage, and the positive electrode material with low working voltage is relative to metal lithium (namely vsLi) + /Li) hasThe electrode potential less than or equal to 3V, such as lithium titanate (1.5V), organic lithium storage material (1.9V), elemental sulfur (2.1V), oxygen (2.8V) or the like, is obviously different from the anode material of commercial lithium ion batteries adopting high working voltages such as lithium iron phosphate (3.4V), nickel cobalt manganese ternary material (3.8V), lithium cobaltate (3.9V) or lithium manganate (4.0V).
The charge and discharge process of the lithium ion battery is the insertion and extraction process of lithium ions: during charging, lithium ions are extracted from the positive electrode and are inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge. The lithium ion battery actually utilizes the concentration difference of lithium ions to store and discharge energy, and the lithium ion battery is fundamentally characterized in that no metallic lithium simple substance exists or a compound containing the metallic lithium simple substance exists. The lithium metal battery is an energy storage system directly adopting elemental lithium (also called metal lithium) as a negative electrode, and the lithium metal battery has essential difference from the lithium ion battery in the charge and discharge process, and the difference lies in the energy conversion form of the negative electrode side in the charge and discharge process: during charging, lithium ions are combined with electrons at the interface of a metal lithium cathode and an electrolyte to be deposited into a metal lithium simple substance, and during discharging, the energy conversion form of the cathode side is based on deposition and stripping of metal lithium essentially, and since no materials such as carbon or silicon are used as storage carriers for lithium ion insertion, the mass of the cathode side of the battery is reduced, so that the battery has extremely high mass energy density (the mass energy density is the ratio of the battery energy to the battery mass).
It should be noted that Lithium batteries (or Lithium secondary batteries and Lithium-based batteries) widely used and referred to in daily life refer to Lithium ion batteries, and Lithium batteries protected by the prior patent also refer to Lithium ion batteries without additional description (i.e. the appearance of Lithium metal negative electrodes, lithium metal batteries, or Lithium metal anode).
The reason why the lithium metal battery is abandoned in the last century is that lithium dendrite is easily generated in the charging process of the lithium metal battery, and the lithium dendrite is broken into dead lithium after growing to a certain degree, so that the utilization rate of active lithium is reduced; the generation of dead lithium can also increase the internal resistance of the battery, so that the capacity of the battery is reduced; lithium ion sourceThe dendrite grows continuously and even pierces the diaphragm, which causes short circuit between the anode and the cathode and thermal runaway. The charging method of the invention is particularly a method for charging the battery when the value of the state of charge (SOC) of the battery is low. The SOC is a ratio of a remaining capacity of the battery after being used for a certain period of time or left unused for a long time to a capacity of a fully charged state thereof, and is represented by a common percentage, wherein the value ranges from 0 to 100%, when the SOC =0, the SOC indicates that the battery is completely discharged, and when the SOC =100%, the SOC indicates that the battery is completely charged. In different application occasions, the requirement for low SOC value is different, and usually the SOC is considered to be less than 50%, which means that the value is low and the battery needs to be charged, the charging process is for recycling the battery, and the process needs to be rapidly charged under a large current condition. For example, the rapid charging goal released by the united states department of energy (DOE) in 2016 is to charge a battery to a SOC of 80% or more in 15 minutes, with a current demand of 10mA · cm for the rapid charging process -2 Large current of (Chang T, kim H, zutter B T, et al. Contacts (adv. Funct. Mater. 30/2020) [ J]. Advanced Functional Materials, 2020, 30(30).)。
The rapid charging process of a lithium metal battery corresponds to a rapid deposition process of lithium ions at the negative electrode, which is a competitive process of the lithium ion deposition rate and the lithium supply rate of the solution at the interface. Studies have shown that (Xiao J. How little lithium dendrites form in liquid batteries [ J ] Science, 2019, 366 (6464): 426-427.) the growth of lithium dendrites results from a lithium ion concentration gradient formed by the slower diffusion of lithium ions in the electrolyte and the electromigration rate. Under the condition of high-current charging (corresponding to rapid deposition of lithium metal), lithium ions at the interface of the negative electrode are rapidly consumed, a lithium ion dissipation layer is generated, and metal lithium tends to grow vertical to the electrode and enters an electrolyte phase to capture lithium ions required by deposition, so that lithium dendrites are generated. Therefore, how to slow down the lithium ion dissipation at the negative electrode interface is the key to stabilize lithium deposition during fast charge.
With the progress of material science and characterization technology in recent decades, the core problem of lithium metal batteries is overcome, and the re-arrangement of the commercial market becomes the impetus of companies including the Ningde era, tesla, and the steam generation. Some scientific papers (e.g., zhang C, wu B, zhou Y, et al, mussel-insulated hydrogels: from design principles to conditioning applications [ J ]. Chemical Society Reviews, 2020, 49.) and patents provide strategies for stabilizing lithium metal deposition: for example, a three-dimensional conductive matrix or a foam matrix is adopted as a deposition framework of lithium (CN 110518254B, CN 110010895B), and the lithium ion flow is homogenized by reducing the local current density, so as to achieve stable deposition of lithium metal under a high current condition. For another example, lithium metal deposition is stabilized using a high-concentration salt electrolyte solution capable of forming a stable solid electrolyte interface film (SEI) (CN 110890592B, CN 111276744A), but the use of a high-concentration salt increases the production cost of the electrolyte solution by several times, making large-scale application difficult. Developing a simple, economical, and efficient method to achieve stable deposition of metallic lithium under rapid charging of lithium metal continues to be a century-old challenge that plagues both academic and industrial circles.
The change of the charging method can reduce the battery charging time and stabilize the battery cycle, however, the charging technology disclosed in the prior art is basically based on the CC-CV charging method (constant current-constant voltage) of the lithium ion battery, which is based on the lithium ion battery charging protocol (Ouyang M]. eTransportation, 2019, 1:100013.；Hussein A H ,Batarseh I . A Review of Charging Algorithms for Nickel and Lithium Battery Chargers[J]IEEE Transactions on Vehicular Technology, 2011, 60 (3): 830-838.), namely, initial constant current charging to a cutoff voltage (CC stage), and constant voltage charging to a small current close to 0 (CV stage). Because different batteries have difference in area size, the current density describes the current magnitude in unit area, and the current density describes the electric signal response when the batteries are charged, the interference of the battery size can be avoided, and the description is more scientific, so that the charging current without special description in the description of the invention refers to the charging current densityIn mA · cm -2 . In the constant voltage Charging (CV) stage, a charged battery is subjected to constant voltage charging, at this time, the charging current generally shows a process of gradually decreasing or increasing first and then decreasing, and the highest value that the charging current density can reach is a peak value of the charging current density, which can be detected and recorded by a current detection unit of the charging device. A specific current value can be set as the off condition of the constant voltage charging by the charging device. Constant current charging refers to an operation of constant current charging of a battery to be charged, wherein the charging current density is constant, the voltage of the battery to be charged at this time shows a gradual increase trend, and a specific voltage value can be set by a battery charging device as a cut-off condition of constant current charging. The later constant voltage process (CV stage) can make the lithium ion concentration distribution in the positive and negative electrode intercalation materials of the lithium ion battery more uniform, and is very important for the positive electrode material to exert 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 charging can slow down the aging of the battery while reducing the charging time, and the purpose of these studies is often to reduce heat generation, avoid lithium evolution or reduce mechanical stress, thereby also creating an MCC-CV method based on CC-CV: it comprises two or more constant current phases followed by a constant voltage phase. The MCC-CV method is also a coupled charging method of initial constant current and subsequent constant voltage, and is classified as the CC-CV method. In addition, the improved lithium ion battery charging method also includes a CP-CV method (constant power-constant voltage charging), a PulseCharging method, a boosting charging method, and a variable current charging method, etc. (see fig. 1).
At present, few charging technologies are specially developed for lithium metal batteries, and the charging mode of the lithium metal batteries refers to a CC-CV method of the lithium ion batteries and a related improved method. In studies of limited lithium metal battery charging technologies, such as US patent US2018/0026464Al, the inventors propose a novel charging method, namely CC 1 -CC 2 CV charging method. This patent utilizes a larger first constantConstant current CC 1 The brief charging is carried out in order to form a layer of initially uniform and stable lithium metal nuclei for the purpose of facilitating smooth growth of the lithium nuclei and thereby suppressing the generation of lithium dendrites, and the patent and literature (Li Z, wang Z L. Special Issue: research highheights in the Beijing Institute of Nanoenergy and Nanosystems [ adv. Funct. Mater. 41/2019) [ J]Advanced Functional Materials, 2019, 29 (41). From the above, the charging method is also basically an MCC-CV method (see (b) in FIG. 1) of initial constant current charging, and is also classified as a CC-CV method. Indeed, the initial large current does favor the Nucleation of Lithium Metal (Pei A, zheng G, shi F, et al. Nanosize Nuclear and Growth of Electrodeposited Lithium Metal [ J)]Nano Letters, 2017, 17 (2): 1132.), also means faster charging speed, but continuous large current charging inevitably results in rapid consumption of lithium ions at the negative electrode interface, generation of a lithium ion dissipative layer, and induction of lithium dendrite growth (Xiao J. How lithium dendrites form in lithium batteries [ J ]]Science, 2019, 366 (6464): 426-427.), whereas the optimal duration of the initial constant current is difficult to define, if the duration is not long enough, it does not play a role in forming abundant nuclei, if the duration is too long, it is rather liable to cause the growth of lithium dendrites and the short-circuiting of the cell.
It is not difficult to find that, in the simple or complex charging method favored by the lithium ion battery, the initial charging stage adopts constant current charging (with a first constant current period), and the difference is nothing about adjusting the initial current or the current step, but the initial constant voltage charging (with a first constant voltage period) is absolutely abandoned, and the reason is mainly two-fold: one, commercial li-ion batteries typically have operating voltages greater than 3.4V, i.e., at least 3.4V above the applied voltage is required to effectively charge the battery. If an initial constant voltage charging is used, the larger voltage may cause structural collapse or even pulverization of positive electrode Materials such as lithium cobaltate (3.9V, layered structure), nickel-cobalt-manganese ternary (3.8V, layered structure) and lithium iron phosphate (3.4V, polyanionic structure) (Masashi Okubo, seong jaeko, debaseita dwibedi. Design positive electrodes with high sensitivity for lithium-ion batteries [ J ]. Journal of Materials Chemistry a, 2021,9 7407-7421 ], resulting in rapid degradation of battery capacity and a significant reduction in battery life. Secondly, in The process of charging The lithium ion battery, if The initial constant voltage charging is adopted, the initial charging current is huge, although The large current means that The charging speed is accelerated, the polarization effect generated by The initial huge current can continuously reduce The potential on The negative electrode side and finally fall below 0V to cause lithium precipitation on The surface of The negative electrode, which affects The service life and even causes safety hazards (Trini, M; J sword large, hauch P, et al. Journal of The Electrochemical energy-resource-Research-Journal of DTU Orbition (09/03/2019)).
In view of the essential difference between the lithium ion battery and the lithium metal battery in the energy storage mechanism explained in the background art, the charging method designed based on the lithium ion battery core problem cannot be directly transplanted into the lithium metal battery to be effective, and even the influence of the two most basic charging structural units of constant voltage and constant current on the deposition of lithium metal is unknown. The inventor finds that the lithium metal battery operated by the standard charging protocol CC-CV is easy to generate lithium dendrite and short circuit under the condition of quick charging and has short service life, so that the system is required to explore the influence of two most basic charging structural units of constant voltage and constant current on lithium metal deposition, and invent a new quick charging method which is specifically suitable for the lithium metal battery to inhibit the generation of the lithium dendrite, which is very important for developing a high-energy quick charging battery system.
Disclosure of Invention
In view of the deficiencies of the prior art, the present inventors propose a novel charging method, which is a first Constant Voltage (CV) 1 ) Charging and subsequent constant Current-constant Voltage (CC-CV) 2 ) The coupling charging method of (1). In the research process, the inventor unexpectedly finds that the charging method breaks through the traditional academic thinking formula, the constant voltage is initially adopted for charging, and the charging method can reduce a negative electrode interface lithium ion dissipation layer, so that lithium metal is deposited to be compact and smooth, the growth of lithium dendrites is inhibited, and the lithium dendrites are effectively protectedThe metal-based electrode prolongs the service life and plays a role in improving the safety of quick charging.
The specific scheme is as follows:
the invention provides a charging method of a lithium metal battery, which is a first Constant Voltage (CV) 1 ) Charge and subsequent constant Current-constant Voltage (CC-CV) 2 ) By coupled charging methods, i.e. CV 1 -CC-CV 2 A charging method, comprising the steps of:
1) Acquiring the actual working voltage and the rated electric quantity of the lithium metal battery to be charged, wherein the value of the actual working voltage is a first Constant Voltage (CV) 1 ) Is provided as a reference, a first Constant Voltage (CV) 1 ) The value of (c) should not be less than +0.2V or not more than +1V, for example, if the operating voltage of the lithium metal/elemental sulfur battery is 2.1V, the applied CV is 1 Value of (2.3V is less than or equal to CV) 1 Less than or equal to 3.1V; the numerical value of the rated electric quantity is used for calculating the state of charge (SOC) of the lithium metal battery to be charged;
2) Starting constant voltage charging with a first Constant Voltage (CV) 1 )；
3) Starting a first Constant Voltage (CV) 1 ) Detecting the charged electric quantity of the lithium metal battery to be charged after charging, wherein the ratio of the charged electric quantity to the rated electric quantity is the state of charge (SOC) of the battery, and the SOC = charged electric quantity/rated electric quantity;
4) Determining whether the battery continues constant voltage charging according to the SOC value, and stopping the first Constant Voltage (CV) when the SOC value exceeds a set value 1 ) Charging;
5) Stopping the first Constant Voltage (CV) 1 ) After charging, converting the charging current into Constant Current (CC) charging;
6) Detecting the voltage or the charged electric quantity of the lithium metal battery to be charged after starting Constant Current (CC) charging, and stopping the Constant Current (CC) charging when the voltage rises to a set voltage value or the SOC exceeds a set value;
7) Stopping constant electricityAfter charging the current (CC), it is converted to a second Constant Voltage (CV) 2 ) Charging;
8) Start the second Constant Voltage (CV) 2 ) Detecting a charging current of the lithium metal battery to be charged after charging, and stopping the second Constant Voltage (CV) when the current drops to a set current value 2 ) Charging, and finishing charging;
said first Constant Voltage (CV) 1 ) And a second Constant Voltage (CV) 2 ) Are equal or different.
By adopting a traditional standard charging protocol (CC-CV stage), lithium ions on an electrolyte-lithium metal negative electrode interface are rapidly consumed when a lithium metal battery is rapidly charged, so that the negative electrode needs to capture the lithium ions to an electrolyte phase during charging, tip lithium metal deposition is generated, and even lithium dendrites grow out to pierce a diaphragm, thereby causing safety accidents. If the first stage of the charging protocol is only high-current charging (i.e. the standard charging protocol CC-CV), the negative electrode side deposits lithium dendrites with fine and sharp morphology, resulting in low utilization rate of active lithium (low coulombic efficiency on the lithium side), severe electrode polarization and capacity attenuation, and even the lithium dendrites continuously grow and finally pierce through the diaphragm to cause short circuit of the battery.
The inventor unexpectedly finds that the initial constant voltage stage is introduced before a standard charging protocol (CC-CV stage), so that the internal electric field of the battery can be strengthened, the lithium ions in the electrolyte can be promoted to migrate to the negative electrode, and the rapid consumption of the interface lithium ions during rapid charging is slowed down.
Wherein the first constant voltage may also be referred to as a first constant voltage, denoted as CV 1 (ii) a The second constant voltage may also be referred to as a second constant voltage, denoted as CV 2 (ii) a The constant current may also be referred to as a constant current, denoted CC.
Preferably, in the step 4), the set value of the state of charge of the battery is 5% -100%, and when the state of charge of the battery is 100%, the constant voltage charging is performed in the whole process correspondingly. The whole-process constant-voltage charging method specifically comprises the following steps:
1) Acquiring the actual working voltage and rated electric quantity of a lithium metal battery to be charged;
2) Starting with a first Constant Voltage (CV) 1 ) Performing constant voltage charging;
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 state of charge (SOC) of the battery;
4) When the value of the state of charge (SOC) of the battery reaches 100%, stopping the constant-voltage charging and finishing the charging; or when the current is reduced to a set current value, the constant voltage charging is stopped, and the charging is finished.
A constant-voltage charging phase including a first constant voltage CV 1 And a second constant voltage CV 2 The set current value mentioned in the above stage is a value to which the current is extremely small, and is usually set to 0.1C or less, and may be 0.05C or less, and may be 0.01C or less. Wherein C is used to represent the charge-discharge capacity rate of the battery. And 1C represents the current intensity at which the battery was completely discharged for one hour. The discharge was completed for 1 hour at 1C intensity for a 18650 cell, which was nominally 2200mA · h, at which time the discharge current was 2200mA.
Preferably, the first constant voltage and the second constant voltage have a value between 1V and 3.5V.
Preferably, the first constant voltage and the second constant voltage are between 1.5 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 is not less than +0.2V and not more than +1V, for example, if the operating voltage of the lithium metal/elemental sulfur battery is 2.1V, the applied CV is 1 Value of (2.3V) or less CV 1 ≤3.1V。
Preferably, the first Constant Voltage (CV) 1 ) The peak value of the current density at the charging stage of (2) is not less than 10mA 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 isThe step constant current comprises at least two current platforms, and the current density of each current platform is 0.01-10 mA-cm -2 。
More preferably, the current density of each current platform is 0.5 to 5 mA-cm -2 。
Preferably, the negative electrode material of the lithium metal battery is a simple substance of metallic lithium or a compound containing the simple substance of metallic lithium. Further, the compound containing the metallic lithium simple substance is selected from a lithium metal alloy or a lithium metal-carbon material.
The lithium metal alloy is selected from any one of lithium aluminum alloy, lithium magnesium alloy, lithium tin alloy, lithium boron alloy and lithium indium alloy.
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-working-voltage positive electrode material, and the voltage of the low-working-voltage positive electrode material is less than or equal to 3V (vs Li) + /Li). The voltage has no absolute value, a reference object is needed, all potentials in the invention are not additionally described, and the potentials of the lithium metal electrode are used as reference, namely vs Li +/Li.
Preferably, the low-operating-voltage positive electrode material is selected from any one of lithium titanate, an 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, the cathode material is pure lithium metal, and the anode material is elemental sulfur.
It should be noted that, for the lithium metal battery, the negative electrode material adopts a simple metal lithium substance or a compound containing a simple metal lithium substance, and the potential of the negative electrode is also determined, so that the working voltage of the battery depends on the type of the positive electrode material (the electrode potential depends on the material property, and can be obtained by a nernst equation or quantum chemical calculation), and the battery in the charging process can be analyzed by a voltmeter, and the actual working voltage is obtained through detection and calculation. Since graphite or silicon containing no lithium source is used as the negative electrode material of the lithium ion battery, the positive electrode material of the lithium ion battery must contain a lithium source for energy conversion, and the positive electrode material is limited to lithium cobaltate (3.9V, layered structure), nickel-cobalt-manganese ternary (3.8V, layered structure), lithium iron phosphate (3.4V, polyanionic structure), and the like (Yang L, yang K, zheng J, et al. Connecting the surface structure to high-performance materials for lithium-ion batteries [ J ]. Chemical Society Reviews, 2020, 49.). In contrast, in the lithium metal battery using lithium metal as the negative electrode, since the negative electrode side already has a lithium source, the positive electrode material may be a positive electrode material containing no lithium source, such as elemental sulfur, oxygen, an organic lithium storage material, or the like, in addition to the above-described positive electrode material containing lithium. The lithium metal battery consisting of the positive electrode of the organic lithium storage material (1.9V), the elemental sulfur (2.1V) or the oxygen (2.8V) and the negative electrode of the lithium metal has low working voltage. The low working voltage means that even if constant voltage charging is adopted, the used voltage value is small, and obvious structural damage to the anode material is avoided; on the other hand, these low-voltage materials are not strictly crystalline substances having a layered structure, an olivine structure, or the like, and there is no fear of the breakdown of the structure by voltage.
The lithium metal battery is formed by respectively taking the anode material and the cathode material as the anode and the cathode and assembling the anode material, the cathode material, the anode material and the cathode material together with an adaptive electrolyte and a diaphragm. Specifically, the constant voltage and constant current basic modules are respectively connected to the assembled lithium metal battery and charged. As a rapid charging method of the lithium metal battery of the present invention, the charging method is a coupling method of an initial Constant Voltage (CV) charge and a subsequent constant current-constant voltage (CC-CV) charge, i.e., CV 1 -CC-CV 2 Provided is a charging method. Wherein the initial constant voltage is a first constant voltage, denoted as CV 1 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 preferable aspect of the rapid charging method of the lithium metal battery of the present invention, the charging voltage CV 1 Value of (1V) is less than or equal to CV 1 3.5V or less, and the SOC reaches 20 percent or more and 100 percent or less under the constant-voltage charging cutoff condition. The SOC (State of charge), i.e., the State of charge of the battery, is used to reflect the remaining capacity of the battery, which is numerically defined as the ratio of the remaining capacity to the battery capacity, expressed as a percentage. The value ranges from 0 to 1, indicating that the battery is completely discharged when SOC =0, and indicating that the battery is completely charged when SOC = 1. Preferably, the charging voltage CV is 1 Value of (1.5V) or less CV 1 ≤3.2V。
Further preferably, the value of the constant current CC is more than or equal to 0.2C and less than or equal to 3C, and the constant current charging cut-off condition is that the voltage is more than or equal to 2.6V. Wherein C is used to represent the charge-discharge capacity rate of the battery. And 1C represents the current intensity at one hour of complete discharge of the battery. The discharge was completed for 1 hour at 1C intensity for a 18650 cell, which was nominally 2200mA · h, at which time the discharge current was 2200mA.
Further preferably, the second constant voltage CV 2 The value is between 1V and 3.5V; preferably, the second constant pressure CV is 2 The value is between 1.5V and 3.2V.
More preferably, the charging voltage CV is 2 2.6V, and the constant voltage charge off condition is a current of less than 0.03C.
Tests of the invention show that CV is adopted 1 -CC-CV 2 Compared with the standard charging protocol CC-CV, the charging method can ensure that the lithium metal deposition is compact and smooth, the growth of lithium metal dendrites is inhibited, the charging speed of the assembled battery is shorter, the cycle is stable, and the service life is prolonged.
The invention also provides a charging device of the lithium metal battery, which adopts the charging method and comprises the following steps:
a power conversion unit providing a Constant Current (CC) and a Constant Voltage (CV) 1 Or CV 2 ) A charging input of (a);
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 voltages at two ends of the battery, the current detection unit is used for detecting the magnitude of current passing through the battery, and the electric quantity detection unit is used for integrating the current and time to obtain electric quantity;
a control circuit controlling an output of the power conversion unit, including a voltage-current conversion unit (CV) 1 Conversion to CC) and a current-voltage conversion unit (CC to CV) ２ ）；
And the human-computer interface interaction module is used for setting specific input values and cut-off conditions of each charging and discharging stage.
The CV is 1 (first constant Voltage) and CV 2 The values of the (second constant voltages) are equal or different.
Specifically, an operator firstly carries out CC-CV-based charging on a charged battery through a human-computer interface interaction module 2 Charging test of the method, constant Current CC and constant Voltage CV 2 Provided by the power conversion unit. After the first circle of charging is finished, the voltage detection unit averages and calculates the voltage in the battery charging process, so that the actual working voltage of the battery is obtained; the electric quantity detection unit integrates the charging current and the time to obtain the electric quantity of the full-charged state of the battery, namely the rated electric quantity of the battery.
Starting CV 1 -CC-CV 2 Charging operation, wherein an operator inputs specific input values and cutoff conditions of each charging and discharging stage through a human-computer interface interaction module, and a first constant voltage CV is provided by a power conversion unit 1 The current detection unit detects the charging current at the stage in real time, and carries out real-time integral conversion on the current and time, the integral result is the charged electric quantity, the ratio of the charged electric quantity to the rated electric quantity of the battery is SOC, and the detection unit also calculates and updates the SOC in real time. Stopping the first Constant Voltage (CV) by a charge control switch when the SOC value exceeds a set value 1 ) And charging and performing Constant Current (CC) charging through the power conversion unit.
The voltage detection unit is used for detecting the voltage of the battery in the CC stage during the charging processDetecting to obtain the real-time voltage of the battery, and stopping charging the Constant Current (CC) when the real-time voltage rises to a set voltage value; alternatively, the Constant Current (CC) charging may also be stopped when the real-time updated SOC value exceeds a set value. Stopping the Constant Current (CC) charging by a charge control switch and performing a second Constant Voltage (CV) by a power conversion unit 2 ) And (6) charging.
Detecting a second Constant Voltage (CV) by a current detecting unit 2 ) And (3) stopping charging the Constant Current (CC) when the current is reduced to a set current value, and finishing charging.
According to the charging device, a coupling method of an initial Constant Voltage (CV) charge and a subsequent constant current-constant voltage (CC-CV) charge of a lithium metal battery, i.e., CV, can be implemented 1 -CC-CV 2 Provided is a charging method.
It should be noted that, compared with the existing charging technology based on lithium ion battery design, the invention proposes to add a section of initial constant voltage charging process, namely, to propose a CV (constant voltage charging) based on the standard charging protocol CC-CV 1 -CC-CV 2 The charging method of (1). The initial constant voltage stage was abandoned as a detrimental effect on commercial lithium ion batteries, whereas in the present invention, it was surprisingly found that the process provides a great improvement in the rapid charging performance of lithium metal batteries.
CV proposed by the invention 1 -CC-CV 2 The method has the beneficial effects that: initial constant pressure stage CV 1 A charge current (fig. 1 (f)) gradually decreasing from high may be generated, facilitating 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 can strengthen the electric field in the battery, promote lithium ions to migrate to the negative electrode with low potential, slow down the dissipation of the lithium ions on the interface of the negative electrode and further ensure that the deposited lithium metal has smooth and compact appearance. The method effectively inhibits the growth of lithium dendrites, thereby simply, conveniently and efficiently protecting the lithium metal electrode, prolonging the service life of the electrode and improving the cycle stability and safety.
Drawings
Fig. 1 is a schematic diagram of voltage and current changes with time in various Charging methods, in which the horizontal axis represents Charging time, and the vertical axis represents both Charging voltage (solid line) and Charging current (dashed line) corresponding thereto, in fig. 1, (a) represents standard constant current-constant voltage (CC-CV) Charging, (b) represents step current-constant voltage (MCC-CV) Charging, (c) represents constant power-constant voltage (CP-CV) Charging in fig. 1, (d) represents Pulse Charging (Pulse Charging) in fig. 1, (e) represents boost Charging (Boosting Charging) in fig. 1, and (f) represents constant voltage-constant current-Constant Voltage (CV) Charging provided by the present invention in fig. 1 1 -CC-CV 2 ) A charging method;
fig. 2 is a graph comparing coulombic efficiencies under constant current and constant voltage deposition conditions for the lithium copper batteries prepared in example 1 and comparative example 1;
FIG. 3 is a graph showing the charge and discharge current curves of the lithium copper battery prepared in example 1 under the constant voltage deposition condition;
FIG. 4 is a plan SEM photograph (left) of deposition of lithium metal under the constant current deposition conditions employed in comparative example 1, and a plan SEM photograph (right) of lithium under the constant voltage deposition conditions employed in example 1 is given;
FIG. 5 shows the results of the lithium-lithium titanate batteries prepared in CC-CV (comparative example 2) and CV 1 -CC-CV 2 (example 2) a graph of characteristic capacity versus charge time under fast charge conditions;
FIG. 6 shows CV of lithium-lithium titanate cell prepared in example 2 1 -CC-CV 2 A charge-discharge current curve chart under the charging condition;
FIG. 7 shows the results of the lithium-sulfur battery prepared at CC-CV (comparative example 3) and CV 1 -CC-CV 2 (example 3) characteristic capacity comparison plot under conditions;
FIG. 8 shows the CC-CV stages and CV of lithium-sulfur batteries prepared from the control in example 5 1 -CC-CV 2 Normalized feature capacity versus plot under staged conditions.
Detailed Description
In order to make the object, technical solution and technical effect of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the examples given in this specification are for the purpose of illustration only and are not intended to limit the invention, which is not limited to the examples given in this specification.
In particular, the invention relates to a quick charging method and a charging device based on a lithium metal battery. The cathode material of the lithium metal battery is a metallic lithium simple substance or a compound containing the metallic lithium simple substance. Further, the compound containing the metallic lithium simple substance is selected from a lithium metal alloy or a lithium metal-carbon material. The lithium metal alloy is selected from any one of lithium aluminum alloy, lithium magnesium alloy, lithium tin alloy, lithium boron alloy and lithium indium alloy. The carbon material is selected from any one of graphite, graphene, carbon nanotubes and carbon nanowires. The lithium ion battery has essential difference from a commercial lithium ion battery adopting a graphite base or a silicon base as a negative electrode in the aspects of energy conversion principle and performance restriction factors. The positive electrode of the lithium metal battery is made of a positive electrode material with low working voltage (less than or equal to 3V vs Li) + Li), such as lithium titanate (1.5V), organic lithium storage material (1.9V), elemental sulfur (2.1V), or oxygen (2.8V), etc., as compared with commercial lithium ion batteries using high-voltage materials such as lithium iron phosphate (3.4V), nickel-cobalt-manganese ternary material (3.8V), lithium cobaltate (3.9V), or lithium manganate (4.0V) as the positive electrode. The charging method is a coupling method of an initial Constant Voltage (CV) charge and a subsequent constant current-constant voltage (CC-CV) charge, i.e. CV 1 -CC-CV 2 Provided is a charging method. Specifically, the charging method first determines the actual operating voltage of the lithium metal battery to be charged (the voltage is determined by the kind of the positive electrode material); then applying a first Constant Voltage (CV) of at least 0.2V greater than the operating voltage 1 ) Performing a charge, the charge cut-off condition of the stage being at least 5% of a state of charge (SOC) of the battery; then coupled with a common standard charging protocol (CC-CV) to perform a normalized charging, wherein the CV in the normalized charging is a second Constant Voltage (CV) 2 ）， CV 1 And CV 2 The numerical values of (c) may be equal or different. Lithium metal batteries rapidly consume lithium ions at the electrolyte-lithium metal negative electrode interface during rapid charging, thereby requiring the negative electrode to move into the electrolyte phase during chargingTrapping lithium ions and producing sharp lithium metal deposits and even growing lithium dendrites that pierce the membrane causing a safety hazard. If the first stage of the charging protocol is only high-current charging (i.e. the standard charging protocol CC-CV), the negative electrode side deposits lithium dendrites with fine and sharp morphology, resulting in low utilization rate of active lithium (low coulombic efficiency on the lithium side), severe electrode polarization and capacity attenuation, and even the lithium dendrites continuously grow and finally pierce through the diaphragm to cause short circuit of the battery. The charging method provided by the invention adopts constant voltage (first constant voltage) charging in the initial stage, and is essentially different from the initial constant current (first constant current) charging in the standard charging method. By utilizing the charging method, an initial constant voltage stage (which has negative influence on the traditional lithium ion battery and is not adopted) is introduced before a standard charging protocol, so that the internal electric field of the battery can be strengthened, the lithium ions in the electrolyte are promoted to migrate to the negative electrode, and the rapid consumption of the interface lithium ions during rapid charging is slowed down.
Comparative example 1
Since lithium metal batteries are different from lithium ion batteries, the influence of two most basic charging structural units, namely constant voltage and constant current, on lithium metal negative electrodes is discussed. Therefore, comparative example 1 and example 1 were first assembled with the same lithium copper battery, and charging thereof corresponds to the process of depositing lithium metal from lithium ions in the electrolyte on the copper current collector, both electrodes would be covered with active lithium metal, and interference of other active materials can be excluded to show the influence of the constant voltage or constant current charging unit on the lithium metal electrode. Since lithium is deposited on copper, the electrodes on both sides are lithium metal, so that the actual working voltage is 0, and the energy storage function is not realized. The lithium copper battery systems in comparative example 1 and example 1 belong to a mechanical research tool, and are only used for eliminating the interference of the positive electrode, and focus on researching the influence of a constant voltage or constant current charging mode on the lithium metal electrode.
Assembling the cathode metal lithium and the anode copper sheet into a lithium copper battery, wherein the electrolyte is 1MLiTFSI/DOL-DME/2%LiNO 3 。
Connecting constant current to carry out charge-discharge cycle test, wherein the conditions are as follows: the deposition current density was 12mA cm -2 The deposited electricity quantity is 1mAh cm -2 The deposition time is 5min; the stripping current was 1 mA/cm -2 . The deposition current density, the deposition electric quantity and the deposition time are the charging current density, the charging electric quantity and the charging time. The deposited electricity quantity is 1mAh cm -2 I.e. the rated charge in example 1.
Through the charge-discharge cycle test, the coulombic efficiency of the lithium-copper battery is rapidly reduced, and is less than 40% after 30 circles.
Example 1
The same cell as comparative example 1 was assembled: assembling the cathode metal lithium and the anode copper sheet into a lithium-copper battery, wherein the electrolyte is 1M LiTFSI/DOL-DME/2% LiNO 3 。
The actual working voltage of the lithium-copper battery is detected and calculated by a charging device and is 0V, and the rated electric quantity is 1mAh cm -2 。
Example 1 is a full range constant voltage charge, the deposition process uses a constant voltage, and the conditions are as follows: the deposition voltage is 0.25V, and the deposition electric quantity is 1mAh cm -2 The average deposition time is less than 5min; stripping current of 1 mA-cm -2 . The deposition electric quantity and the deposition time are the charging electric quantity and the charging time.
Constant voltage deposition is constant voltage charging, corresponding to CV 1 -CC-CV 2 CV in the method 1 ，CV 1 The value is the actual working voltage of the battery plus 0.25V, namely CV 1 Is 0.25V; and CV is 1 The condition of the end of the stage is that the SOC reaches 100 percent, which corresponds to the constant voltage charging in the whole process.
Through the test of charge-discharge cycle, the lithium metal battery is charged with constant voltage under the condition in the embodiment, and the peak current of charge is more than 16 mA-cm -2 At least 40 cycles are circulated and the coulombic efficiency is kept above 90%.
Fig. 2 shows a graph comparing the coulombic efficiency of a lithium copper battery under constant current and constant voltage deposition of lithium. Fig. 3 gives the corresponding current diagram for constant voltage charge and discharge conditions. Fig. 4 gives planar scanning electron micrographs of metallic lithium under the constant voltage deposition conditions of comparative example 1 and example 1, respectively. It can be seen from the observation of the graph that, in the constant voltage deposition process of example 1, the surface of the lithium metal electrode is more compact and smooth compared with the constant current condition, and tends to planar growth, inhibiting the generation of lithium dendrites.
Comparative example 2
Assembling a lithium metal-based battery (lithium-lithium titanate battery) by using a thin metal lithium sheet with the thickness of 45 mu m as a negative electrode and a positive electrode lithium titanate pole piece, wherein the percentage of the electrolyte is 1MLiTFSI/DOL-DME/2 LiNO 3 。
The charge-discharge cycle test is carried out according to the CC-CV protocol in the prior art under the following conditions: constant current charging with a charging current multiplying factor of 6C (1C about 0.935mA cm) -2 ) When the voltage reaches 3V, the constant voltage charging is changed into 3V constant voltage charging, and the cut-off condition in the constant voltage stage is that the current is less than 0.03C; the discharge multiplying power is 2C, and the charge-discharge interval is 1-3V (vsLi) + /Li). Since the batteries of comparative example 2 and example 2 were the same two batteries, they had the same actual operating voltage and rated capacity. The charging device charges the battery of comparative example 2 by the CC-CV method (i.e., CC-CV) 2 Charging of the method), the voltage detection unit performs an averaging calculation on the first-turn charging voltage of the battery in the comparative example 2, thereby obtaining the actual working voltage of the battery; the electric quantity detection unit performs integral conversion on the first-turn charging current and the time of the battery in the comparative example 2 to obtain the electric quantity of the full-charged state of the battery, namely the rated electric quantity. Through a charge-discharge cycle test, the lithium source of the cathode of the lithium-lithium titanate battery is rapidly consumed, and the capacity begins to rapidly decrease after 40 circles.
Example 2
The same cell as comparative example 2 was assembled: thin metal lithium sheets with the thickness of 45 mu M are used as a negative electrode and a positive lithium titanate electrode sheet to assemble 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 and is 1.55V (vs Li) + /Li)) the rated capacity is the rated capacity described in comparative example 2.
Using CV of 1 -CC-CV 2 Protocol charging and cycle testing are carried out under the following conditions: constant voltage charging, charging voltage CV 1 The value is the actual working voltage of the battery plus 0.35V, namely 1.9V (vs Li) + /Li)。
Example 2 is a full-range constant voltage charge, the charge cutoff condition is that the charge current density is less than a minimum value, i.e., less than 0.03C, and then the single-turn charge is stopped for discharging; the discharge multiplying power is 2C, and the discharge interval is 1-3V (vs Li) + /Li)。
Through the charge-discharge cycle test, the lithium metal battery is charged with constant voltage under the conditions in the embodiment, and the peak current reaches 27mA cm in the constant voltage stage -2 The cell was cycled at least 100 cycles, the capacity remained stable, and the charge time was reduced to half that of comparative example 2, approximately 3 minutes.
Fig. 5 is a graph comparing the characteristic capacity and the charging time of lithium-titanate batteries under charging conditions of comparative example 2 and example 2. Example 2 the original CV was used 1 -CC-CV 2 The charging method, the battery, the capacity of which remained stable at 100 cycles, whereas the battery of comparative example 2, which employed the CC-CV method, started to significantly fade in capacity after 45 cycles. In addition, from the viewpoint of charging time, the charging time of the battery in the example was shortened to within 3 minutes of stability, whereas the charging time of the battery in the comparative example exceeded 6 minutes within 45 cycles of the stabilization cycle.
Fig. 6 shows a charge-discharge current profile of a lithium-lithium titanate battery in the case of example 2. Viewing the graph, it can be found that at CV 1 -CC-CV 2 In the charging process, the peak current of charging is as high as 27mA cm -2 The charging time can be greatly shortened.
Comparative example 3
Assembling a lithium metal battery using a thin metal lithium sheet having a thickness of 45 μm as a negative electrode and a positive electrode as a sulfur sheet, the electrolyte being 1MLiTFSI/DOL-DME/2% 3 。
And (3) carrying out charge-discharge cycle test by adopting a CC-CV protocol under the following conditions: after the battery is cycled stably (i.e. the capacity is kept stable, and the cycle number is more than 50 circles), the charging current multiplying power is converted from 0.2C to 1C (1C is about 3.33mA cm) -2 ) When the voltage reaches 2.6V, the constant voltage charging is changed into 2.6V,the cut-off condition of the constant voltage stage is that the current is less than 0.03C, the discharge process is that the constant current discharges at 0.2C, and the charge-discharge interval is 1.8-2.6V (vs Li) + /Li). Since the batteries of comparative example 3 and examples 3 and 4 were the same three batteries, they had the same actual operating voltage and rated charge. The charging device charges the battery in the comparative example 3 by a CC-CV method, and the voltage detection unit averages and calculates the first-circle charging voltage of the battery in the comparative example 3 so as to obtain the actual working voltage of the battery; the electric quantity detection unit performs integral conversion on the first-turn charging current and the time of the battery in the comparative example 3 to obtain the electric quantity of the full-charged state of the battery, namely the rated electric quantity. Through the charge-discharge cycle test, the lithium source of the lithium-sulfur battery cathode is rapidly consumed, and the capacity is gradually reduced circle by circle.
Example 3
The same cell as comparative example 3 was assembled: a thin metal lithium sheet with the thickness of 45 mu M is used as a negative electrode and a positive electrode sulfur sheet to assemble a lithium metal-based battery, and the electrolyte is 1M LiTFSI/DOL-DME/2% LiNO 3 。
The actual working voltage of the lithium-sulfur battery is detected and calculated by the charging device and is 2.1V (vs Li) + /Li)), the rated electric quantity is the rated electric quantity described in comparative example 3.
Charging using CV 1 -CC-CV 2 Method, cycle testing was performed under the following conditions: constant voltage charging, charging voltage CV 1 The value is the actual working voltage of the battery plus 0.45V, namely 2.55V (vs Li) + /Li)。
Example 3 is a full-range constant voltage charge, the charge cutoff condition is that the charge current density is less than a minimum value, i.e., less than 0.03C, and then the single-turn charge is stopped for discharging; the discharge stage is 0.2C constant current discharge, and the discharge interval is 1.8-2.6V (vs Li) + /Li)。
Through the charge-discharge cycle test, the lithium metal battery is subjected to constant voltage charging under the conditions in the embodiment, the capacity is kept stable, the quick charging life is at least 70 circles, and the charging time is kept within 12 min.
FIG. 7 shows the CC-CV and CV values of lithium-sulfur batteries 1 -CC-CV 2 Characteristic capacity versus charge. The observation picture canIt is found that in CV 1 -CC-CV 2 During charging, the capacity hardly decays.
Example 4
The same cell as comparative example 3 was assembled by using a thin metal lithium sheet of 45 μ M thickness as the negative and positive electrode sulfur sheets to form a lithium metal cell, and the electrolyte was 1M LiTFSI/DOL-DME/2% LiNO 3 。
The actual working voltage of the lithium-sulfur battery is detected and calculated by the charging device and is 2.1V (vs Li) + /Li)) the rated capacity is the rated capacity described in comparative example 3.
Charging using CV 1 -CC-CV 2 The method comprises performing a cycle test on a LAND electrochemical test device under the following conditions: constant voltage charging, charging voltage CV 1 The value is the actual working voltage of the battery plus 0.7V, namely 2.8V (vs Li) + /Li)。
Example 4 is a full-time constant voltage charge, the charge cutoff condition is that the charge current density is less than a minimum value, i.e., less than 0.05C, and then the single-turn charge is stopped for discharging; the discharge stage is 0.2C constant current discharge, and the discharge interval is 1.8-2.6V (vs Li) + /Li). Through the charge-discharge cycle test, the lithium metal battery is subjected to constant voltage charging under the conditions in the embodiment, and the capacity is kept stable.
Example 5
Thin metal lithium sheets with the thickness of 45 mu M are used as a negative electrode and a positive electrode sulfur pole piece to be assembled into a lithium metal battery, and electrolyte is 1M LiTFSI/DOL-DME/2% LiNO 3 。
Further increasing the voltage value in the initial constant voltage stage can increase the charging current to reduce the charging time, and increasing the voltage value to 2.6V in example 3 in example 5 can further reduce the charging time. The greater current that results tends to short the cell, requiring a reduced CV at this point 1 -CC-CV 2 Middle initial CV 1 The contributed SOC to avoid battery short circuits. This example will use a self-control approach to CV pairing 1 -CC-CV 2 The charging superiority will be explained.
And (3) performing a charge-discharge cycle test by adopting a CC-CV protocol under the following conditions: CC charging currentThe multiplying power is 0.5C, when the voltage reaches 2.6V, the constant voltage charging is changed into 2.6V, the cut-off condition of the constant voltage stage is that the current is less than 0.03C, the discharging process is 0.2C constant current discharging, and the charging and discharging interval is 1.8-2.6V (vs Li + /Li). The actual working voltage of the lithium-sulfur battery is detected and calculated by a charging device and is 2.1V (vs Li +/Li)), and the rated electric quantity is the first full charge electric quantity in the CC-CV charging process.
The battery capacity is completely stable after 50 circles and is changed into CV after 60 circles 1 -CC-CV 2 The charging is carried out by the following method: constant voltage charging, charging voltage CV 1 The value is the actual working voltage of the battery plus 0.5V, namely 2.6V (vs Li) + /Li)，CV 1 Stopping the first constant voltage charging after the SOC of the stage reaches 50%, and converting the SOC into CC constant current charging, wherein the CC charging current multiplying power is 0.5C; when the voltage of the CC stage reaches 2.6V, stopping the constant-current charging, and changing the constant-current charging into 2.6V second constant-voltage charging; when the second constant voltage charging CV 2 The current of the stage is less than 0.03C, the single-circle charging is completed, the stage is converted into discharging, the discharging process is 0.2C constant current discharging, and the charging and discharging interval is 1.8-2.6V (vs Li) + /Li). This process is repeated for cyclic charging and discharging.
FIG. 8 shows the CC-CV and CV values of lithium-sulfur batteries 1 -CC-CV 2 Normalized characteristic capacity versus charge. As can be seen from the figure, the CV was changed from the control experiment 1 -CC-CV 2 After the method (after 60 circles), the charging and discharging capacity of the battery is improved by nearly 40% in the CC-CV stage. The dynamic performance of the surface lithium metal cathode 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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