Formation method of lithium-free negative electrode battery

Abstract

The invention relates to a formation method of a lithium-free negative electrode battery, and belongs to the technical field of lithium batteries. The testing method comprises the following steps: standing at low temperature before first-circle charging to enable the interior of the battery to reach a steady state, carrying out short-time and low-electric-quantity charging by adopting large current, and charging and discharging for several circles by adopting small current after the interior of the battery reaches the steady state at room temperature. According to the formation process provided by the invention, a compact seed crystal layer formed by lithium cores can be formed on the surface of Cu in situ at low temperature and high current density, so that the physical binding force between a deposited lithium layer and a copper substrate is remarkably enhanced, and the contact resistance is reduced, thereby inhibiting the growth of moss or dendritic metal lithium and realizing low-porosity and high-compactness lithium deposition; and a more uniform and stable SEI film is formed through low-current deposition, so that the coulombic efficiency and the cycling stability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-free anode batteries, and particularly to a formation method for a lithium-free anode battery. Background Art

[0002] The theoretical specific capacity of metallic lithium is 3860 mAh / g, which is more than 10 times that of the theoretical specific capacity of conventional graphite anode materials (372 mAh / g). Moreover, it itself has excellent electrical conductivity. Therefore, it is an ideal battery anode material, with important research value and application prospects. However, during the use of metallic lithium anodes, problems such as metallic lithium dendrites and dead lithium occur, which not only seriously affect the cycling performance of lithium metal batteries but also pose serious safety hazards. As a new generation of battery system, lithium-free anode batteries are proposed. Their anodes have no excessive lithium, and all lithium sources come entirely from the cathode material. Compared with the lithium metal battery system, the proportion of lithium content in the battery system is greatly reduced, and its safety is greatly improved.

[0003] Lithium-free anode batteries have the following major advantages: (1) Since there is no additional highly chemically active substance such as metallic lithium in the anode, the production cost is greatly reduced and the safety is increased. (2) There is no need to use anode active materials, and they have extremely high volumetric energy density and mass energy density. (3) They are compatible with existing battery production processes and do not require additional production processes. Therefore, lithium-free anode batteries have a higher energy density and a cost-effective manufacturing process.

[0004] However, during the cycling process of lithium-free anode batteries, they completely rely on the lithium deintercalated from the cathode material during the first charge. Therefore, their commercialization faces key technical challenges: their service life is usually short because the inhomogeneous lithium nucleation and growth caused by the inherent incompatibility of lithium with copper current collectors lead to the formation of dead lithium during the cycling process, resulting in a rapid decrease in the content of active lithium, ultimately causing no capacity contribution and battery failure; more importantly, the low Coulomb efficiency is the main reason hindering their entry into the commercial market.

[0005] Research has found that the formation of dead lithium is not only related to the electrolyte and cathode and anode materials in the battery system, but different test conditions also have an important impact.

[0006] Therefore, it is necessary to develop an efficient and reasonable test method to effectively alleviate the rapid capacity decay during the battery cycling process, improve the cycling life of lithium-free anode batteries, and enhance their application potential. Summary of the Invention

[0007] Aiming at the defects existing in the above-mentioned prior art, the object of the present invention is to propose a formation method for a lithium-free anode battery; by standing at a low temperature before the first charge to make the inside of the battery reach a steady state, a large current is used for short-time and low-capacity charging, and after the inside of the battery reaches a steady state at room temperature, small current charge and discharge are carried out for several cycles to complete; solve the problem of uneven deposition caused by the incompatibility of lithium with copper during the formation stage of the lithium-free anode battery, thereby reducing the loss caused by dead lithium, effectively alleviating the capacity attenuation during the battery cycle, and extending the battery cycle life.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A formation method for a lithium-free anode battery, the formation method comprising the following steps:

[0010] S1: Stand at a low temperature before the first charge to make the inside of the battery reach a steady state, use a large current for short-time charging during the first charge, and use a small current for discharging during the first discharge;

[0011] S2: After the first charge ends, stand at room temperature to make the inside of the battery reach a steady state, and carry out small current charge and discharge for several cycles.

[0012] As a preference of the above formation method, the negative electrode of the battery is composed of a copper current collector, the positive electrode is a lithium-containing material, and the electrolyte is a liquid electrolyte.

[0013] Through the coordinated cooperation of the steps of the above formation method, not only the nucleation and growth potential of subsequent lithium deposition are effectively reduced, but also the physical binding force between the deposited lithium layer and the copper substrate is significantly enhanced, the contact impedance is reduced, thereby inhibiting the growth of moss or dendritic metallic lithium, and realizing low-porosity and high-density lithium deposition. The SEI formed on the lithiumophilic substrate is dense and uniform, and its thickness is close to the theoretical value, having a high packing density and a small porosity. It helps to form an SEI film with a smaller resistance and a larger capacitance, thereby improving the Coulomb efficiency and cycle stability of the battery, and large current stripping can reduce the thickness and resistance of the SEI film.

[0014] As a preference of the above formation method, the temperature of the low temperature condition in step S1 is -25 to 10 °C; further preferably the temperature is -15 to 5 °C; more preferably the temperature is more preferably -5 to 5 °C, and more preferably 0 °C.

[0015] As a preference of the above formation method, the standing time in step S1 is 4 hours or more; further preferably the standing time is 5 to 10 hours; more preferably the standing time is 7 hours.

[0016] As a preference of the above formation method, for the large current charging in step S1, the charging current is 1C to 5C; further preferably the charging current is 1 to 3C; more preferably the charging current is 1C.

[0017] As a preference of the above formation method, for the large-current charging in step S1, the charging time is 30 to 120 s; more preferably, the charging time is 45 to 90 s; even more preferably, the charging time is 55 - 65 s.

[0018] As a preference of the above formation method, for the small-current discharging in step S1, discharge to the cut-off voltage of 3 V, and the discharging current is below 0.8C; more preferably, the discharging current is 0.05 - 0.7C; even more preferably, the discharging current is 0.1 - 0.5C.

[0019] As a preference of the above formation method, for the room-temperature condition in step S2, the temperature is 15 - 30 °C; more preferably, the temperature is 20 - 25 °C; even more preferably, the temperature is 25 °C.

[0020] As a preference of the above formation method, for the standing time in step S2, it is 4 hours or more; more preferably, the standing time is 5 - 10 hours; even more preferably, the standing time is 7 hours.

[0021] As a preference of the above formation method, for the charging cut-off voltage in step S2, it is 4.1 - 4.4 V, and the discharging cut-off voltage is 2.5 - 3 V; more preferably, the charging cut-off voltage is 4.2 - 4.4 V, and the discharging cut-off voltage is 2.8 - 3.2 V; even more preferably, the charging cut-off voltage is 4.3 V, and the discharging cut-off voltage is 3 V.

[0022] As a preference of the above formation method, for the number of small-current charge-discharge cycles in step S2, it is 2 - 6 cycles; more preferably, the number of charge-discharge cycles is 2 - 5 cycles; even more preferably, the number of charge-discharge cycles is 3 cycles.

[0023] As a preference of the above formation method, in the small-current charge-discharge in step S2, the charge-discharge conditions for each cycle can be the same or different, with a charging rate of 0.03 - 0.06C and a discharging rate of 0.03 - 0.06C; preferably, the charging rate is 0.03 - 0.06C and the discharging rate is 0.03 - 0.06C.

[0024] As a preference of the above formation method, for the number of small-current charge-discharge cycles in step S2, it is 3 cycles, and the mode is AAB (i.e., the first and second charge-discharge cycles are in mode A, and the third charge-discharge cycle is in mode B), where in mode A, the charging rate is 0.03 - 0.06C and the discharging rate is 0.03 - 0.06C; in mode B, the charging rate is 0.03 - 0.06C and the discharging rate is 0.1 - 0.53C.

[0025] As a further preference, the copper current collector is a copper foil current collector, a copper foam-based current collector, or a copper nanofiber network. More preferably, the negative electrode is a current collector that has been modified. Even more preferably, it is a current collector coated with a lithium-philic coating.

[0026] As a further preference, the lithium-containing material is lithium iron phosphate, lithium manganese iron phosphate, ternary lithium, lithium cobaltate, lithium manganate, lithium-rich layered material, etc.

[0027] As a further preference, the electrolyte components include one or more of LIFSI, LITFSI, DME, LiBF 4 , FEC, DEC, DOL, TTE, LiDFOB.

[0028] As a further preference, conventional separator materials can be used in the above-mentioned battery. For example, ceramic-coated separators (single-sided ceramic separators, double-sided ceramic separators), single-layer PP / PE separators, and three-layer PP / PE / PP. The use of the separator can increase the porosity and meet the requirements of rapid ion migration at high rates and high liquid absorption rate in step S1.

[0029] Advantages of the present invention:

[0030] Compared with the related art, the present invention has the following advantages:

[0031] (1) In the present invention, by standing at a low temperature before the first charge to make the inside of the battery reach a steady state, charging with a large current for a short time and a low charge amount, and then using a small current to charge and discharge several cycles after reaching a steady state at room temperature, combined with the selection of specific materials such as the positive and negative electrodes and electrolyte of the battery, this helps to form a SEI film with a smaller resistance and a larger capacitance, thereby improving the Coulomb efficiency and cycle stability of the battery. The large-current stripping can reduce the thickness and resistance of the SEI film. Therefore, it can reduce the loss caused by dead lithium, effectively alleviate the attenuation of the capacity during the battery cycle, and extend the battery cycle life.

[0032] (2) In step S1, a dense seed layer composed of lithium nuclei with a diameter of about 50-200 nm can be in-situ formed on the Cu surface at a low temperature and a high current density. This not only effectively reduces the nucleation and growth potential of subsequent lithium deposition, but also significantly enhances the physical bonding force between the deposited lithium layer and the copper substrate, reduces the contact impedance, thereby inhibiting the growth of moss or dendritic metallic lithium and realizing low-porosity and high-density lithium deposition.

[0033] (3) In step S2, a uniformly distributed lithium metal (Li) metal nucleus is deposited on the surface of the Cu current collector substrate after standing, reducing the influence of the substrate on further lithium deposition: the uniform and dense ultra-thin lithium deposition layer overcomes the thermodynamic limitation of the copper substrate; the increased contact area and bonding strength effectively reduce the contact impedance and stimulate the uniform distribution of the local current density on the current collector; a large number of lithium nuclei provide the maximum sites for subsequent lithium metal nucleation and growth.

[0034] (4) In step S2, a thin SEI with good mechanical stability is formed through a small-current charge-discharge process. Depositing at a small current on the treated substrate, the SEI formed on the lithiophilic substrate is dense and uniform, and its thickness is close to the theoretical value, with a high packing density and a small porosity; at a low current density, Li 2 CO 3 is formed first, while ROCOO-Li (the substance formed by the reaction of ROCOOH and Li+) starts to form only before the end of the electrode discharge. Description of the Drawings

[0035] Figure 1 SEM image of the in-situ seed layer by the formation method of Example 1 of the present invention. Detailed Embodiments

[0036] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below. However, it should be understood that the description herein is only used to explain the present invention and is not intended to limit the scope of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The characterization means involved herein can refer to the relevant descriptions in the prior art and will not be elaborated herein.

[0038] Specific meanings of the abbreviations of the present invention:

[0039] LiFSI, lithium bis(fluorosulfonyl)imide, CAS registration number 171611-11-3;

[0040] LiTFSI, lithium bis(trifluoromethanesulfonyl)imide, CAS registration number 90076-65-6;

[0041] DME, ethylene glycol dimethyl ether;

[0042] LiBF 4 , lithium tetrafluoroborate;

[0043] LiPF 6 , lithium hexafluorophosphate;

[0044] FEC, fluoroethylene carbonate;

[0045] DEC, diethyl carbonate;

[0046] DMC, dimethyl carbonate;

[0047] DOL, 1,3-dioxolane;

[0048] TTE, 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether;

[0049] PVDF, polyvinylidene fluoride;

[0050] LiDFOB, lithium difluoroborate oxalate.

[0051] To further understand the present invention, the following provides a more detailed description of the present invention in conjunction with the best embodiments.

[0052] Example 1:

[0053] Battery fabrication: The positive electrode material is ternary material (NCM811); the negative electrode material is smooth copper foil; the electrolyte is 6.5M lithium bis(fluorosulfonyl)imide (LiFSI), and the solvent is a mixed system of ethylene glycol dimethyl ether (DME): 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether (TTE) (1:4 v / v); the separator is a single - sided ceramic separator. A single - layer soft - pack battery is assembled in a glove box filled with argon to obtain the NCM811 - Cu - 1 full battery. In this example, the 1C current rate corresponds to a current density of 2.5 mA / cm 2 .

[0054] (1) Preparation of the positive electrode sheet: The dry powders of lithium nickel cobalt manganese oxide, carbon nanotubes, and PVDF are stirred and slurried with a solvent in a mass ratio of 98:1:1, stirred for 6 hours to obtain a slurry with a viscosity of 5500 - 8500 Pa·S, and then coated, dried, roll - pressed, and slit on aluminum foil to fabricate the positive electrode sheet.

[0055] (2) The copper foil is slit to fabricate the negative electrode sheet.

[0056] The above - mentioned positive electrode sheet, separator, and negative electrode sheet are stacked into an electric core, with the separator located between the positive electrode sheet and the negative electrode sheet. The separator faces the negative electrode sheet with a coating. After hot - pressing, tab welding, and aluminum - plastic film encapsulation, a small soft - pack lithium - metal battery core without a negative electrode is made, with a capacity of 150 mAh.

[0057] The formation method steps are as follows:

[0058] S1: The test electric core is placed in a low - temperature test chamber and left to stand for 7 h at a temperature of 0 °C until the inside of the electric core reaches a steady state. Then, it is charged at a constant current of 1C for 60 s.

[0059] S2: The battery is left to stand at room temperature of 25 °C for 7 h until the inside reaches a steady state. The voltage range: the charge cut - off voltage is 4.3 V, and the discharge cut - off voltage is 3 V. Then, it is cycled twice at 0.05C / 0.05C and once at 0.05C / 0.1C.

[0060] The processed battery cells are subjected to charge-discharge cycles with a current rate of 0.2C / 1C and a voltage range where the charge cut-off voltage is 4.3V and the discharge cut-off voltage is 3V. The cycle life of the processed NCM811-Cu battery cells is almost twice that of the unprocessed ones, reaching over 100 cycles, and the average Coulombic efficiency is 99.65%.

[0061] As Figure 1 shown Figure 1 is the scanning electron microscope (SEM) image of the in-situ seed layer prepared by the formation method used in Example 1 of the present invention. It can be observed from the figure that the surface of the in-situ seed layer presents a granular structure with uniform distribution, indicating that the seed particles are successfully deposited on the substrate surface and form a relatively dense layered structure. The size and distribution of the particles in the image show the good uniformity and adhesion of the seed layer, which helps to improve the growth quality and compactness of the SEI film during the subsequent formation process.

[0062] Note: "Unprocessed" refers to the battery formed by the ordinary method and charged and discharged at 0.1C at room temperature.

[0063] Example 2

[0064] Battery manufacturing: A lithium metal battery without a negative electrode, with the positive electrode material being LiNi 0.8 Co 0.1 Mn0 .1 O 2 (NCM811), the negative current collector is a smooth copper foil. The electrolyte is 1.0M lithium hexafluorophosphate (LiPF6), the solvent is a mixed system of dimethyl carbonate (DMC): ethylene carbonate (EC) (2:1 v / v); the separator is a double-sided ceramic separator. A single-layer soft-pack battery is assembled in a glove box filled with argon to obtain the NCM811-Cu-2 full battery. In this example, a 1C current rate corresponds to a current density of 4 mA / cm 2 . The steps of its formation method are as follows:

[0065] S1: The tested battery cell is placed in a low-temperature test chamber and left to stand for 7 hours at a temperature of 0°C until the inside of the cell reaches a steady state. Then, it is charged at a constant current rate of 1C for 60S.

[0066] S2: The battery is left to stand at room temperature of 25°C for 7 hours until the inside reaches a steady state, with a voltage range where the charge cut-off voltage is 4.3V and the discharge cut-off voltage is 3V, 0.05C / 0.1C, and then cycled twice, and 0.05C / 0.2C for one cycle.

[0067] The processed battery cells are subjected to charge-discharge cycles at a current rate of 0.2C / 1C, with a voltage range of 3.0 - 4.3V. The charging cut-off voltage is 4.3V, and the discharging cut-off voltage is 2.8V. The processed NCM811-Cu-2 anode-free battery can stably cycle 60 times with an average Coulombic efficiency of 98.5%.

[0068] Example 3

[0069] Battery manufacturing: An anode-free lithium metal battery with the cathode material being LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), and the anode current collector is a smooth copper foil. The electrolyte is an ester-based electrolyte system of 0.6M LiDFOB and 0.6M LiBF 4 , with the solvent being a mixed system of fluoroethylene carbonate (FEC): diethyl carbonate (DEC) (v / v 1:2); the positive and negative electrodes and the electrolyte are assembled into a single-layer soft-pack battery in a glove box filled with argon to obtain the NCM811-Cu-3 full battery. The injection volume is 3g / Ah; the separator is a single-layer PP / PE separator. The formation method steps are as follows:

[0070] S1: The test battery cell is placed in a low-temperature test chamber and left to stand for more than 7 hours at a temperature of 0°C until the inside of the battery cell reaches a steady state. Then, it is charged at a constant current of 1C for 60 seconds.

[0071] S2: The battery is left to stand at room temperature (25°C) for more than 7 hours until the inside reaches a steady state, and then it is cycled at 0.05C / 0.05C with a voltage range of 4.3V for the charging cut-off voltage and 3V for the discharging cut-off voltage for two cycles, and then cycled at 0.05C / 0.1C for one cycle.

[0072] The processed battery cells are subjected to charge-discharge cycles at a current rate of 0.2C / 1C, with a voltage range of 3.0 - 4.3V. The processed NCM811-Cu-3 battery cells can stably cycle 90 times with a Coulombic efficiency of 99.6%.

[0073] Example 4

[0074] To meet the actual requirements, the formation method of this application is used for mass-producing 17Ah-class battery cells.

[0075] Battery manufacturing: An anode-free lithium metal battery with the cathode material being ternary material (NCM811); the anode material is a double-sided smooth copper foil; the electrolyte is 6.5M lithium bis(fluorosulfonyl)imide (LiFSI), and the solvent is a mixed system of ethylene glycol dimethyl ether (DME): 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) (1:4 v / v); the separator is a three-layer PP / PE / PP.

[0076] The positive and negative electrode materials and the electrolyte are produced into the finished product battery cell NCM811-Cu-4 on the production line.

[0077] The formation method steps are as follows: S1: The test battery cell is placed in a low-temperature test chamber and left to stand for more than 7 hours at a temperature of 0 °C until the inside of the battery cell reaches a steady state. Then, it is charged at a constant current of 1 C for 60 s.

[0078] S2: The battery is left to stand at room temperature for more than 7 hours until the inside reaches a steady state. Then, it is charged and discharged at 0.05 C / 0.05 C, with the voltage range: the charging cut-off voltage is 4.3 V, and the discharging cut-off voltage is 3 V, for two cycles, and then charged and discharged at 0.05 C / 0.1 C for one cycle.

[0079] The cycle life of the 17 Ah soft-pack non-negative electrode battery after the above tests can still reach about 60 weeks at a voltage range of: the charging cut-off voltage is 4.3 V, the discharging cut-off voltage is 3 V, and a rate of 0.2 / 1 C, with an average Coulombic efficiency of 99.73%. It meets the customer's performance requirements.

[0080] Example 5:

[0081] Battery production: The non-negative electrode lithium metal battery configuration is adopted, the positive electrode material is the lithium-rich positive electrode Li 2 Ni 0.5 Mn 1.5 O 4 (LMO), the negative electrode current collector is a smooth copper foil. The electrolyte is 1.0 M lithium hexafluorophosphate (LiPF6), and the solvent is a mixed system of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) (1:1:1 v / v / v); the separator is a double-sided ceramic separator. The single-layer soft-pack battery is assembled in a glove box filled with argon to obtain the LMO-Cu-1 full battery. In this example, the 1 C current rate corresponds to a current density of 2 mA / cm 2 . The formation method steps are as follows:

[0082] S1: The test battery cell is placed in a low-temperature test chamber and left to stand for more than 10 hours at a temperature of 5 °C until the inside of the battery cell reaches a steady state, and then it is charged at a constant current of 2 C for 70 s.

[0083] S2: The battery is left to stand at room temperature of 25 °C for 10 hours until the inside reaches a steady state, with the voltage range: the charging cut-off voltage is 4.4 V, the discharging cut-off voltage is 3.3 V. Then, it is charged and discharged at 0.06 C / 0.06 C for two cycles, and then charged and discharged at 0.06 C / 0.53 C for one cycle.

[0084] The battery cell after the above treatment is charged and discharged in cycles, with a current rate of 0.2 C / 1 C and a voltage range of the charging cut-off voltage of 4.5 V and the discharging cut-off voltage of 3 V. The treated LMO-Cu-1 battery can be stably cycled 250 times. The average Coulombic efficiency is 99.76%.

[0085] Example 6

[0086] Battery manufacturing: non - negative - electrode lithium - metal battery, the positive - electrode material is lithium - rich (Li.Ni.Mn.O); the negative - electrode material is double - sided polished copper foil; the electrolyte is 6.5M LiFSI (lithium bis(fluorosulfonyl)imide), and the solvent is a mixed system of ethylene glycol dimethyl ether (DME): 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether (TTE) (1:4 v / v); the separator is a double - sided ceramic separator. Assemble the positive and negative electrodes and the electrolyte in a glove box filled with argon to form a single - layer soft - pack LMO - Cu - 2 full battery, and the injection volume is 3 g / Ah.

[0087] After the following treatments:

[0088] S1: Put the test battery cell into a low - temperature test chamber, stand still at - 5°C for 4 hours until the inside of the battery cell reaches a steady state. Then charge at a constant current rate of 1C for 45 s.

[0089] S2: Let the battery stand still at 25°C for 4 hours until the inside reaches a steady state. The voltage range: the charge - cut - off voltage is 3.6V, and the discharge - cut - off voltage is 2.0V. Then cycle at 0.02C / 0.05C for two cycles and 0.05C / 0.1C for one cycle.

[0090] The battery cells treated as above are subjected to charge - discharge cycles, the current rate is 0.2C / 1C, and the voltage range: the charge - cut - off voltage is 4.3V, and the discharge - cut - off voltage is 3V. In the lithium - rich material system, the LMO - Cu - 2 battery cells treated by this invention can be stably cycled 200 times, and the average Coulomb efficiency is 99.76%. Relatively excellent cycling performance is obtained.

[0091] Example 7

[0092] Battery manufacturing: non - negative - electrode lithium - metal battery, the positive - electrode material is a lithium - rich (Li.Ni.Mn.O) system, and the negative - electrode current collector is a polished copper foil. The electrolyte is an ester - based electrolyte system of 0.6M LiDFOB (lithium difluoro(oxalato)borate) and 0.6M LiBF 4 , the solvent is a mixed system of fluoroethylene carbonate (FEC): diethyl carbonate (DEC) (v / v 1:2); the separator is a double - sided ceramic separator; assemble the positive and negative electrodes and the electrolyte in a glove box filled with argon to form an LMO - Cu - 3 full battery by single - layer soft - pack battery assembly. The injection volume is 3 g / Ah. The steps of its formation method are as follows:

[0093] S1: Put the test battery cell into a low - temperature test chamber and stand still for more than 7 h at 0°C until the inside of the battery cell reaches a steady state. Then charge at a constant current rate of 1C for 60 s.

[0094] S2: Leave the battery to stand at room temperature of 20 °C for more than 7 h until it reaches a steady state inside, then perform 0.05C / 0.05C charge and discharge cycles with a voltage range of a charge cut-off voltage of 4.3 V and a discharge cut-off voltage of 3 V for two cycles, and then perform one cycle of 0.05C / 0.1C charge and discharge cycles.

[0095] Perform charge and discharge cycles on the battery cells processed as above with a current rate of 0.2C / 1C and a voltage range of a charge cut-off voltage of 4.65 V and a discharge cut-off voltage of 3 V. The processed LMO-Cu-3 battery cells can be stably cycled 180 times, with an average Coulombic efficiency of 99.66%.

[0096] Example 8

[0097] To meet the demand for higher energy density, the formation method of this application is used for mass-producing 15 Ah-class battery cells. Battery manufacturing: a lithium metal-free battery without a negative electrode, with a cathode material being a lithium-rich material (Li.Ni.Mn.O); the anode material is a double-sided polished copper foil; the electrolyte is 6.5 M lithium bis(fluorosulfonyl)imide (LiFSI), and the solvent is a mixed system of ethylene glycol dimethyl ether (DME): 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) (1:4 v / v); the separator is a double-sided ceramic separator.

[0098] Produce the cathode and anode materials and the electrolyte into a finished battery cell LMO-Cu-4 on the production line.

[0099] Then conduct tests: S1: Place the test battery cell in a low-temperature test chamber and leave it to stand for more than 7 h at a temperature of 0 °C until the inside of the battery cell reaches a steady state. Then perform constant-current charging at a current rate of 1C for 60 s.

[0100] S2: Leave the battery to stand at room temperature of 25 °C for more than 7 h until it reaches a steady state inside, then perform 0.05C / 0.05C charge and discharge cycles with a voltage range of a charge cut-off voltage of 4.3 V and a discharge cut-off voltage of 3 V for two cycles, and then perform one cycle of 0.05C / 0.1C charge and discharge cycles.

[0101] The cycle life of the lithium-rich system 15 Ah soft-pack lithium metal-free battery after the above tests can still reach more than 90 weeks at a voltage range of a charge cut-off voltage of 4.3 V and a discharge cut-off voltage of 3 V and a rate of 0.2 / 1C, with an average Coulombic efficiency of 99.70%.

[0102] Comparative example:

[0103] The specific settings are shown in Table 1. Finally, perform charge and discharge cycles on the processed battery cells with a current rate of 0.2C / 1C and a voltage range of a charge cut-off voltage of 4.3 V and a discharge cut-off voltage of 3.0 V. The stable cycle times and average Coulombic efficiency of the battery are shown in Table 1.

[0104] Table 1 Setting Conditions and Product Data of Comparative Examples

[0105]

[0106]

[0107] Conclusion:

[0108] Examples 1 - 8 exhibited better cycling performance than Comparative Examples 1 - 7, indicating that the formation method of the present invention can effectively improve the cycling performance of the lithium metal anode-free battery, and the average Coulombic efficiency is greater than 98%. Specifically, when comparing Example 1 with Comparative Example 1, NCM811-Cu was subjected to the same experimental operations at a low temperature (0 °C) before the first charge cycle. The cycle life and average Coulombic efficiency of NCM811-Cu were significantly higher than those of NCM811-Cu-1 under the conditions of Comparative Example 1. The reasons include at least two aspects. On the one hand, the low-temperature standing before the first charge significantly increases the viscosity of the electrolyte, increasing the migration resistance of lithium ions, thereby improving the migration selectivity of lithium ions. This means that the migration of lithium ions in the electrolyte is more orderly, reducing the interference of other ions and improving the migration efficiency of lithium ions. Furthermore, it weakens the concentration polarization effect and can stabilize the electrode surface, so the diffusion and deposition effect of lithium ions can be adjusted. On the other hand, at a high current density during the first large-current charge, it can not only reduce the interfacial energy and enhance the growth of two-dimensional layered metallic lithium, but also effectively disperse the local stress caused by the volume expansion, avoiding local fracture or pore formation, promoting the stable accumulation of rigid crystal nuclei, and finally forming a dense seed layer, enhancing the mechanical stability of the lithium metal anode-free battery. When comparing Example 1 with Comparative Example 2, if the standing temperature before the first charge is too low, it will hinder ion diffusion, resulting in too large internal resistance of the battery. The too low ambient temperature also has an adverse effect on the desolvation process of lithium ions. The desolvation process is a key step for lithium ions to break away from the solvation sheath and participate in the electrode reaction. At a lower temperature, the desolvation energy barrier of lithium ions increases, resulting in an increase in charge transfer resistance and a significant enhancement of the polarization effect, which is not conducive to the formation of a dense SEI film. At too low a temperature, the electrochemical window of the electrolyte may become narrow. This means that the electrolyte is more likely to decompose at low temperatures, and even lead to the precipitation of lithium salts in the electrolyte, causing irreversible effects on the battery cycling performance.

[0109] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A formation method for a lithium-free negative electrode battery, the formation method comprising the following steps: S1: Before the first charge, the battery is left to stand at low temperature to allow the battery to reach a steady state. The first charge uses a large current for a short time, and the first discharge uses a small current. S2: After the first cycle of charging is completed, the battery is left to stand at room temperature to allow the battery to reach a steady state, and then charged and discharged for several cycles using a small current.

2. The chemical formation method according to claim 1, characterized in that: Low temperature conditions in step S1: The temperature is -25 to 10°C; more preferably, the temperature is -15 to 5°C; and / or The standing time in step S1 is 4 hours or more; more preferably, the standing time is 5 to 10 hours.

3. The chemical formation method according to claim 1, characterized in that: High current charging in step S1: The charging current is 1C to 5C; more preferably, the charging current is 1 to 3C; and / or The charging time is 30 to 120 seconds; more preferably, the charging time is 45 to 90 seconds.

4. The chemical formation method according to claim 1, characterized in that: The room temperature conditions in step S2 are: the temperature is 15-30°C; more preferably, the temperature is 20-25°C; The standing time in step S2 is 4 hours or more; more preferably, the standing time is 5 to 10 hours; and more preferably, the standing time is 7 hours.

5. The chemical formation method according to claim 1, characterized in that: In step S2, the charge cut-off voltage is 4.1-4.4V, and the discharge cut-off voltage is 2.5-3.3V; more preferably, the charge cut-off voltage is 4.2-4.4V, and the discharge cut-off voltage is 2.8-3.2V.

6. The chemical formation method according to claim 1, characterized in that: The number of small current charge and discharge cycles in step S2 is 2 to 6 cycles; more preferably, the number of charge and discharge cycles is 2 to 5 cycles; and more preferably, the number of charge and discharge cycles is 3 cycles.

7. The chemical formation method according to claim 1, characterized in that: In the low current charge and discharge of step S2, the charge and discharge conditions of each cycle are the same or different, with a charge rate of 0.03 to 0.06C and a discharge rate of 0.03 to 0.06C.

8. The chemical formation method according to claim 9, characterized in that: The number of cycles of small current charging and discharging in step S2 is 3 cycles, including 2 cycles of charging and discharging at a rate of 0.03-0.06C / 0.03-0.06C; and 1 cycle of charging and discharging at a rate of 0.03-0.06C / 0.1-0.53C.

9. The chemical formation method according to claim 1, characterized in that: The negative electrode of the battery is composed of a copper current collector, and the positive electrode is a lithium-containing material.

10. The chemical formation method according to claim 9, characterized in that: The copper current collector is a copper foil current collector, a foam copper-based current collector, or a fiber network-like nano-copper; the lithium-containing material is lithium iron phosphate, lithium iron manganese phosphate, ternary lithium, lithium cobalt oxide, lithium manganese oxide, or a lithium-rich layered material; the electrolyte components include one or more of LiFSI, LiTFSI, DME, LiBF4, FEC, DEC, DOL, TTE, and LiDFOB.

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