Formation method of a negative electrode-free lithium metal battery

Abstract

The present application relates to a kind of formation method of negative electrode-free lithium metal battery, belong to the method or device technical field for directly converting chemical energy into electrical energy.The formation method of negative electrode-free lithium metal battery of the present application includes the following steps: S1, the cell is placed at temperature T0 Rest, rest time is t0;S2, without applying pressure to the cell, at temperature T0 With current density I0 To the cell is pulsed charged for total duration t1;S3, the temperature of the cell is restored to room temperature;S4, at pressure P1, temperature T1 To the cell is charged and discharged cycle;S5, at pressure P2, 25 ℃ To the cell is charged and discharged cycle;Wherein, -15 ℃≤T0<25 ℃, I0≤2.2C, P1≤2.2N / m, P2≤P1, T1≥30 ℃.The formation method can improve the cycle performance of negative electrode-free lithium metal battery.

Description

Technical Field

[0001] This invention relates to the field of methods or apparatus for directly converting chemical energy into electrical energy, and more particularly to a method for forming a negative electrode-free lithium metal battery. Background Technology

[0002] The development of traditional lithium-ion batteries is limited by the low specific capacity of graphite anodes. While lithium metal batteries use high-capacity lithium metal anodes, they require pre-stored excess lithium, resulting in lower energy density, higher cost, and lower battery safety due to issues such as lithium dendrite growth. Anode-less designs eliminate the excess lithium in the anode, relying solely on the positive electrode lithium source to deposit metallic lithium in situ on the anode current collector during the first charge, theoretically achieving a mass energy density greater than 400 Wh / kg.

[0003] However, negative electrode-free lithium metal batteries have the following problems: 1) Due to the low affinity between the current collector and lithium, lithium nucleation occurs with varying sizes and uneven growth during deposition, which further grows into lithium dendrites, affecting battery safety; 2) "Dead lithium" is continuously generated during cycling - that is, lithium that has lost its electrochemical activity, which rapidly consumes the active lithium content; when the active lithium is exhausted, the battery can no longer provide a usable capacity and eventually fails; 3) The first-cycle and average coulombic efficiency are low, hindering its actual energy output. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for forming a negative electrode-free lithium metal battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for forming a negative electrode-free lithium metal battery, which includes the following steps:

[0007] S1. Place the battery cell at temperature T0 and let it stand for a time t0.

[0008] S2. Without applying pressure or temperature T0 to the battery cell, perform pulse charging on the battery cell with a current density I0 for a total duration of t1.

[0009] S3. Return the temperature of the battery cell to room temperature (approximately 25°C).

[0010] S4. Under pressure P1 and temperature T1, the battery cell is subjected to charge and discharge cycles;

[0011] S5. Under pressure P2 and temperature of 25°C, the battery cell is subjected to charge and discharge cycles.

[0012] Among them, -15℃≤T0<25℃, I0≤2.2C, P1≤2.2N / m, P2≤P1, T1≥30℃.

[0013] This invention effectively reduces the disorder of active lithium arrangement in the electrolyte through low-temperature pretreatment, minimizing the impact of concentration gradient and concentration polarization on the initial deposition and promoting uniform lithium deposition. Furthermore, pulse charging with an appropriate current density effectively promotes the formation of uniformly distributed spherical nucleation sites for lithium metal in the early stages of deposition. Simultaneously, deposition at suitable pressure and temperatures above room temperature not only accelerates lithium ion migration rate and increases ion transference number, resulting in more uniform lithium deposition and a dense, flat deposition layer, but also effectively reduces the nucleation barrier during lithium deposition, preventing localized concentrated nucleation and suppressing dendrite formation. Additionally, it enhances the diffusion energy of active lithium, making the lithium metal deposition-removal-regeneration process smoother, reducing dead lithium accumulation, and thus improving the cycle performance of electrodeless lithium metal batteries.

[0014] It should also be noted that the pressure P1 in step S4 refers to the pressure applied to the battery cell by the pressure clamp, and the pressure P2 in step S5 refers to the pressure applied to the battery cell by the pressure clamp.

[0015] In some implementations, T0 may be, but is not limited to, -15°C, -14°C, -13°C, -12°C, -11°C, -10°C, -9°C, -8°C, -7°C, -6°C, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, or 20°C, or fall within the range of any two of the above values.

[0016] In some implementations, t0 may be, but is not limited to, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h, 6.5h, 7.0h, 7.5h, 8.0h, 8.5h, 9.0h, 9.5h, or 10.0h, or fall within the range of any two of the above values.

[0017] In some implementations, I0 may be, but is not limited to, 2.2C, 2.1C, 2.0C, 1.9C, 1.8C, 1.7C, 1.6C, 1.5C, 1.4C, 1.3C, 1.2C, 1.1C, 1.0C, 0.9C, 0.8C, 0.7C, 0.6C, 0.5C, 0.4C, 0.3C, 0.2C, 0.1C, 0.08C, 0.06C, 0.04C, 0.02C, or 0.01C, or fall within the range of any two of the above values.

[0018] In some implementations, t1 may be, but is not limited to, 90s, 100s, 110s, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, 290s, 300s, 310s, 320s, 330s, 340s, 350s, 360s, 370s, 380s, 390s, or 400s, or fall within the range of any two of the above values.

[0019] In some implementations, P1 may be, but is not limited to, 2.2 N / m, 2.1 N / m, 2.0 N / m, 1.9 N / m, 1.8 N / m, 1.7 N / m, 1.6 N / m, 1.5 N / m, 1.4 N / m, 1.3 N / m, 1.2 N / m, 1.1 N / m or 1.0 N / m, or fall within the range of any two of the above values.

[0020] In some implementations, T1 may be, but is not limited to, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, or 80°C, or fall within the range of any two of the above values.

[0021] In some implementations, P2 may be, but is not limited to, 0.2 N / m, 0.3 N / m, 0.4 N / m, 0.5 N / m, 0.6 N / m, 0.7 N / m, 0.8 N / m, 0.9 N / m, 1.0 N / m, 1.1 N / m, 1.2 N / m, 1.3 N / m, 1.4 N / m, 1.5 N / m, 1.6 N / m, 1.7 N / m, 1.8 N / m, 1.9 N / m, or 2.0 N / m, or fall within the range of any two of the above values.

[0022] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, at least one of the following conditions (1) to (7) is satisfied:

[0023] (1) -10℃≤T0≤10℃;

[0024] (2) 2h≤t0≤8h;

[0025] (3) 0.05C≤I0≤1.5C;

[0026] (4) 100s≤t1≤350s;

[0027] (5)1.2N / m≤P1≤1.9N / m;

[0028] (6) 35℃≤T1≤70℃;

[0029] (7)0.5N / m≤P2≤1.9N / m.

[0030] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, at least one of the following conditions (1) to (7) is satisfied:

[0031] (1) -5℃≤T0≤5℃;

[0032] (2) 3h≤t0≤5h;

[0033] (3) 0.1C≤I0≤1C;

[0034] (4) 110s≤t1≤300s;

[0035] (5)1.5N / m≤P1≤1.8N / m;

[0036] (6) 40℃≤T1≤60℃;

[0037] (7)0.7N / m≤P2≤1.8N / m.

[0038] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, step S4 specifically involves: under pressure P1 and temperature T1, the cell is charged with constant current and constant voltage at current density I1 to the first cutoff voltage V1, and the constant voltage charging state of V1 is maintained for time t3; then, the cell is charged with constant current and constant voltage at current density I2 to the second cutoff voltage V2, with a cutoff current of 0.01C, and left to stand for 20 to 30 minutes; then, the cell is discharged with current density I3 to the cutoff voltage V3, and this charge-discharge cycle is repeated N times.

[0039] By using segmented charging, the current and voltage at different stages can be precisely controlled to optimize the formation quality and consistency of the SEI film, thereby improving the overall performance of the battery. T1 is the thermal formation temperature. Temperature T1 is more conducive to accelerating the stabilization and growth of the SEI film. Excessive temperature may cause electrolyte decomposition. P1 is the clamping pressure of the first stage of formation charging. Excessive pressure will compress the membrane pores and hinder ion transport. Insufficient pressure will lead to a loose battery structure, poor interface contact, and high internal resistance, resulting in uneven current inside the cell. I1 and I2 are the current densities of the segmented formation charging. I1 is to ensure uniform nucleation, while I2 is to ensure uniform lithium ion deposition, making the SEI film denser and more stable. I3 is the discharge current density. At this current density, unstable components can be effectively dissolved, self-healing can be promoted, and cycle life can be improved. In this process, I3 > I1 > I2. The first stage of formation charging to V1 can better complete the main interface film formation and build a "buffer platform" for the high-voltage stage. The second stage charging to V2 is to activate the battery's maximum capacity under the initial interface protection and complete the final stabilization of the high-voltage interface. When discharged to V3, the positive and negative electrode materials return to a more thermodynamically stable intermediate state, significantly reducing their chemical activity and minimizing the risk of internal short circuits and thermal runaway. The number of formation cycles N is used to stabilize the electrode interface and strengthen the SEI / CEI film. A small N value results in an unstable SEI / CEI film, while a large N value will excessively consume the active material, leading to an initial capacity value that is lower than the theoretical capacity value.

[0040] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, at least one of the following conditions (1) to (8) is satisfied:

[0041] (1) 0.05C≤I1≤1C, preferably 0.08C≤I1≤0.8C, more preferably 0.1C≤I1≤0.5C, for example, I1 can be, but is not limited to, 0.05C, 0.08C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C or 1C, or within the range of any two of the above values;

[0042] (2) 3.8V≤V1≤4.1V, preferably 3.85V≤V1≤4.05V, more preferably 3.9V≤V1≤4V, for example, V1 can be, but is not limited to, 3.8V, 3.85V, 3.9V, 3.95V, 4V, 4.05V or 4.1V, or within the range of any two of the above values;

[0043] (3) 1min≤t3≤30min, preferably 2min≤t3≤20min, more preferably 5min≤t3≤15min, for example, t3 can be, but is not limited to, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min or 30min, or within the range of any two of the above values;

[0044] (4) 0.01C≤I2≤0.5C, preferably 0.02C≤I2≤0.33C, more preferably 0.03C≤I2≤0.25C, for example, I2 can be, but is not limited to, 0.01C, 0.02C, 0.03C, 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.35C, 0.4C, 0.45C or 0.5C, or within the range of any two of the above values;

[0045] (5) 4.2V≤V2≤4.4V, preferably 4.25V≤V2≤4.35V, more preferably 4.3V≤V2≤4.35V, for example, V2 can be, but is not limited to, 4.2V, 4.25V, 4.3V, 4.35V or 4.4V, or within the range of any two of the above values;

[0046] (6) 0.05C≤I3≤3C, preferably 0.08C≤I3≤2C, more preferably 0.1C≤I3≤1C, for example, I3 can be, but is not limited to, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, 0.2C, 0.4C, 0.8C, 1C, 1.5C, 2C, 2.5C or 3C, or within the range of any two of the above values;

[0047] (7) 2.6V≤V3≤3.4V, preferably 2.7V≤V3≤3.3V, more preferably 2.8V≤V3≤3.2V, for example, V3 can be, but is not limited to, 2.6V, 2.7V, 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V or 3.4V, or within the range of any two of the above values;

[0048] (8) 1≤N≤10, preferably 2≤N≤8, more preferably 3≤N≤5. For example, N can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, or be within the range of any two of the above values.

[0049] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, step S5 specifically involves: charging the cell at a constant current density of 0.1C to 0.33C to the cutoff voltage of 4.3V under pressure P2 and 25°C, and then discharging it at a constant current density of 0.5C to 1C to the cutoff voltage of 3V.

[0050] In some implementations, the current density of constant current charging may be, but is not limited to, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, or 0.33C, or fall within the range of any two of the above values.

[0051] In some implementations, the current density of the constant current discharge may be, but is not limited to, 0.5C, 0.55C, 0.6C, 0.65C, 0.7C, 0.75C, 0.8C, 0.85C, 0.9C, 0.95C, or 1C, or fall within the range of any two of the above values.

[0052] In a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, the pulse interval time of pulse charging in step S2 is t2 and the pulse charging frequency is f; 1s≤t2≤5s, 1Hz≤f≤50Hz.

[0053] In some implementations, the pulse interval time t2 is preferably 1s≤t2≤4s, more preferably 2s≤t2≤3s, for example, it can be, but is not limited to, 1s, 2s, 3s, 4s or 5s, or within the range of any two of the above values.

[0054] In some embodiments, the pulse charging frequency f is preferably 5Hz≤f≤30Hz, more preferably 10Hz≤f≤20Hz, for example, it can be, but is not limited to, 1Hz, 2Hz, 3Hz, 4Hz, 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, 10Hz, 15Hz, 20Hz, 25Hz, 30Hz, 35Hz, 40Hz, 45Hz or 50Hz, or within the range of any two of the above values.

[0055] In a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, the cell includes a positive electrode, a negative electrode and an electrolyte; the electrolyte includes a lithium salt and an organic solvent.

[0056] The lithium salt includes, but is not limited to, at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium difluoroborate oxalate;

[0057] The organic solvent includes, but is not limited to, at least one of ethylene glycol dimethyl ether, ethylene carbonate, ethyl propionate, vinylene carbonate, fluoroethylene carbonate, diethyl carbonate, 1,3-dioxolane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and tetrahydrofuran.

[0058] In a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, the positive electrode includes a positive electrode active material, which includes, but is not limited to, at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium-rich layered materials.

[0059] In a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, the negative electrode includes a negative electrode current collector, which includes, but is not limited to, any one of copper foil current collector, copper-zinc plated current collector, copper-nickel plated current collector, and copper-silver plated current collector; preferably, at least one side surface of the negative electrode current collector is provided with a carbon coating layer.

[0060] As a preferred embodiment of the formation method of the negative electrode-free lithium metal battery of the present invention, the cell further includes a separator, which includes, but is not limited to, any one of a single-sided alumina-coated separator, a double-sided alumina-coated separator, a single-sided PVDF-coated separator, a double-sided PVDF-coated separator, a PP separator, and a PE separator.

[0061] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0062] This invention effectively reduces the disorder of active lithium arrangement in the electrolyte through low-temperature pretreatment, minimizing the impact of concentration gradient and concentration polarization on the initial deposition and promoting uniform lithium deposition. Furthermore, pulse charging with an appropriate current density effectively promotes the formation of uniformly distributed spherical nucleation sites for lithium metal in the early stages of deposition. Simultaneously, deposition at suitable pressure and temperatures above room temperature not only accelerates lithium ion migration rate and increases ion transference number, resulting in more uniform lithium deposition and a dense, flat deposition layer, but also effectively reduces the nucleation barrier during lithium deposition, preventing localized concentrated nucleation and suppressing dendrite formation. Additionally, it enhances the diffusion energy of active lithium, making the lithium metal deposition-removal-regeneration process smoother, reducing dead lithium accumulation, and thus improving the cycle performance of electrodeless lithium metal batteries. Detailed Implementation

[0063] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0064] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0065] <Testing Methods>

[0066] 1) First Coulomb Efficiency (CE1): At room temperature (the first cycle of the room temperature cycling stage is the first efficiency cycle), the voltage test range is 3.0V to 4.3V, and the charge and discharge cycle test is performed with a current density of 0.2C (charge) / 1C (discharge). First Coulomb Efficiency (CE1) = (first discharge capacity / first charge capacity) × 100%.

[0067] 2) Capacity retention: At room temperature (25℃), the voltage test range is 3.0V to 4.3V, and charge-discharge cycle tests are performed with a current of 0.2C (charge) / 1C (discharge); the capacity C0 is obtained from the first discharge cycle (the first cycle at room temperature), and the capacity C is obtained from the discharge cycle N. N Capacity retention rate = C N / C0×100%; Average coulombic efficiency (%) = (CE1+CE2+CE3+...+CE) N ) / N,CE N Let the Coulomb efficiency be the Coulomb efficiency of the Nth cycle. The Coulomb efficiency of the Nth cycle = (discharge capacity of the Nth cycle / charge capacity of the Nth cycle) × 100%.

[0068] Example 1

[0069] <Preparation of Negative-Electrode Lithium Metal Batteries>

[0070] Positive electrode sheet: Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride (PVDF), conductive carbon black (SP) and carbon nanotubes (CNT) are mixed in a mass ratio of 97:1.5:0.5:1 and mixed evenly with an appropriate amount of NMP to form a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, and after drying, rolling and cutting, the positive electrode sheet is obtained.

[0071] Negative electrode: Carbon-coated copper foil is used as the negative electrode, and the carbon coating thickness of the carbon-coated copper foil is 5μm.

[0072] Separator (single-sided alumina-coated separator): Alumina slurry (by mass percentage, consisting of 15% alumina + 2% polyacrylic acid binder + 1% ammonium polyacrylate dispersant + 0.3% sodium carboxymethyl cellulose thickener and the balance water) is uniformly coated onto one side of a PE separator with a thickness of 12μm using a coating machine, resulting in a coating thickness of 2μm. After drying, the separator is obtained.

[0073] Electrolyte: The lithium salts are lithium difluorosulfonyl imide (LiFSI) and lithium difluoroborate oxalate (LiDFOB), and the solvent is composed of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 1:2, wherein the concentration of LiFSI is 1.2M and the concentration of LiDFOB is 0.2M.

[0074] Negative electrode-free lithium metal battery: The soft-pack battery is assembled in an argon-filled glove box. The positive electrode, negative electrode, and separator are stacked together to form a cell. The separator is located between the positive and negative electrode, with the coated side of the separator facing the positive electrode. After hot pressing, tab welding, and aluminum-plastic film encapsulation, the cell is obtained. The cell is baked in an 85°C oven for 48 hours to remove water. Then, the electrolyte is injected into the cell and it is encapsulated. The electrolyte injection coefficient is 3.5 g / Ah.

[0075] <Formation Method of Negative-Electrode Lithium Metal Batteries>

[0076] S1. Place the above-mentioned battery cell in a constant temperature chamber, adjust the temperature inside the chamber to 0°C, and let it stand for 3 hours to reduce the disorder and diffusion rate of active lithium in the electrolyte so as to facilitate initial deposition.

[0077] S2. Without external clamps, the cell is pulse-charged at a current density of 1C for 120s to form uniform initial nucleation sites on the negative current collector side. The pulse interval is 2s and the pulse frequency is 10Hz.

[0078] S3. Return the temperature of the battery cell to room temperature (25°C) to restore the electrolyte to a low viscosity and high fluidity state for subsequent formation steps;

[0079] S4. Place the battery cell in a pressure fixture with a pressure of 1.8 N / m. Charge it at a constant current and constant voltage of 0.1 C at a temperature of 45°C until the first cutoff voltage of 4.0 V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C until the second cutoff voltage of 4.3 V. The cutoff current is 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0 V. Repeat this process 3 times.

[0080] S5. Reduce the pressure of the pressure clamp to 0.8 N / m, adjust the temperature to room temperature, and then perform constant current charge-discharge cycles at a current density of 0.2C (charging) / 1C (discharging). The charging cut-off voltage is 4.3V and the discharging cut-off voltage is 3.0V.

[0081] Example 2

[0082] Except for step S1 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0083] Step S1 specifically involves placing the battery cell in a constant temperature chamber, adjusting the temperature inside the chamber to 5°C, and allowing it to stand for 5 hours to reduce the disorder and diffusion rate of active lithium in the electrolyte for initial deposition.

[0084] Example 3

[0085] Except for step S1 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0086] Step S1 specifically involves placing the battery cell in a constant temperature chamber, adjusting the temperature inside the chamber to -10℃, and allowing it to stand for 5 hours to reduce the disorder and diffusion rate of active lithium in the electrolyte for initial deposition.

[0087] Example 4

[0088] Except for step S4 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0089] Step S4 is as follows: Place the battery cell in a pressure fixture, set the pressure to 1.8 N / m, and charge it at a constant current and constant voltage of 0.1 C at a temperature of 60°C until the first cutoff voltage of 4.0 V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C until the second cutoff voltage of 4.3 V, with a cutoff current of 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C until it reaches 3.0 V. Repeat this process 3 times.

[0090] Example 5

[0091] Except for step S2 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0092] Step S2 specifically involves: without external clamps, the cell is pulse-charged at a current density of 0.2C for 300s to form uniform initial nucleation sites on the negative current collector side, with a pulse interval of 2s and a pulse frequency of 10Hz.

[0093] Example 6

[0094] Except for step S4 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0095] Step S4 is as follows: Place the battery cell in a pressure fixture, set the pressure to 1.8 N / m, and charge it at a constant current and constant voltage of 0.33 C at a temperature of 45℃ until the first cutoff voltage of 4.0V. Maintain the constant voltage charging state at this voltage for 5 minutes, and then charge it at a constant current and constant voltage of 0.1 C until the second cutoff voltage of 4.3V. The cutoff current is 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0V, and repeat this process 3 times.

[0096] Example 7

[0097] Except for step S4 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0098] Step S4 is as follows: Place the battery cell in a pressure fixture, set the pressure to 1.8 N / m, charge it at a constant current density of 0.05 C to the cutoff voltage of 4.3 V at a temperature of 45 °C, let it rest for 30 min, and then discharge it at a current density of 0.1 C to 3.0 V. Repeat this process 3 times.

[0099] Comparative Example 1

[0100] Except for the <formation method of negative electrode-free lithium metal battery>, which differs from Example 1, the rest is the same as Example 1;

[0101] The <Formation Method of Negative-Electrode Lithium Metal Batteries> includes the following steps:

[0102] At room temperature (25℃), the battery cell is first charged with a constant current and constant voltage at a current density of 0.1C to the cutoff voltage of 4.3V. It is then left to stand at 40℃ for 48 hours and discharged with a current density of 0.1C to the cutoff voltage of 3.0V. Then, a constant current charge-discharge cycle is performed with a current density of 0.2C (charging) / 1C (discharging), with a charging cutoff voltage of 4.3V and a discharging cutoff voltage of 3.0V.

[0103] Comparative Example 2

[0104] Except for the <formation method of negative electrode-free lithium metal battery>, which differs from Example 1 (i.e., the pulse charging step is not performed), the rest is the same as Example 1;

[0105] The <Formation Method of Negative-Electrode Lithium Metal Batteries> includes the following steps:

[0106] S1. Place the above-mentioned battery cell in a constant temperature chamber, adjust the temperature inside the chamber to 0°C, and let it stand for 3 hours to reduce the disorder and diffusion rate of active lithium in the electrolyte so as to facilitate initial deposition.

[0107] S2. Return the temperature of the battery cell to room temperature (25°C) to restore the electrolyte to a low viscosity and high fluidity state for subsequent formation steps;

[0108] S3. Place the battery cell in a pressure fixture with a pressure of 1.8 N / m. Charge it at a constant current and constant voltage of 0.1 C at a temperature of 45°C until the first cutoff voltage of 4.0 V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C until the second cutoff voltage of 4.3 V. The cutoff current is 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0 V. Repeat this process 3 times.

[0109] S4. Reduce the pressure of the pressure clamp to 0.8 N / m, adjust the temperature to room temperature, and then perform constant current charge-discharge cycles at a current density of 0.2C (charging) / 1C (discharging). The charging cut-off voltage is 4.3V and the discharging cut-off voltage is 3.0V.

[0110] Comparative Example 3

[0111] Except for step S2 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0112] Step S2 specifically involves: without external clamps, performing pulse charging on the battery cell at a current density of 3C for 120 seconds to form uniform initial nucleation sites on the negative electrode current collector side, with a pulse interval of 2 seconds and a pulse frequency of 10Hz.

[0113] Comparative Example 4

[0114] Except for step S1 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0115] Step S1 specifically involves placing the battery cell in a constant temperature chamber, adjusting the temperature inside the chamber to -20°C, and allowing it to stand for 3 hours to reduce the disorder and diffusion rate of active lithium in the electrolyte for initial deposition.

[0116] Comparative Example 5

[0117] Except for step S4 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0118] Step S4 is as follows: Place the battery cell in a pressure fixture, set the pressure to 2.5 N / m, and charge it at a constant current and constant voltage of 0.1 C at a temperature of 45°C until the first cutoff voltage of 4.0 V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C until the second cutoff voltage of 4.3 V, with a cutoff current of 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0 V. Repeat this process 3 times.

[0119] Comparative Example 6

[0120] Except for step S4 in the <Formation Method of Negative Electrode-Free Lithium Metal Battery>, which is different from Example 1, the rest is the same as Example 1;

[0121] S4. Place the battery cell in the pressure fixture, set the pressure to 1.8 N / m, and charge it at room temperature (25℃) with a constant current and constant voltage of 0.1 C to the first cutoff voltage of 4.0 V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C to the second cutoff voltage of 4.3 V, with a cutoff current of 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0 V. Repeat this process 3 times.

[0122] Comparative Example 7

[0123] Except for the <formation method of negative electrode-free lithium metal battery>, which differs from Example 1 (i.e., no low-temperature pretreatment step is performed), the rest is the same as Example 1;

[0124] The <Formation Method of Negative-Electrode Lithium Metal Batteries> includes the following steps:

[0125] S1. At room temperature and without external clamps, the cell is pulse-charged at a current density of 1C for 120s to form uniform initial nucleation sites on the negative current collector side. The pulse interval is 2s and the pulse frequency is 10Hz.

[0126] S2. Place the battery cell in a pressure fixture, set the pressure to 1.8 N / m, and charge it at a constant current and constant voltage of 0.1 C at a temperature of 45℃ until the first cutoff voltage of 4.0V. Maintain the constant voltage charging state at this voltage for 5 minutes. Then charge it at a constant current and constant voltage of 0.05 C until the second cutoff voltage of 4.3V, with a cutoff current of 0.01 C. After resting for 30 minutes, discharge it at a current density of 0.1 C to 3.0V. Repeat this process 3 times.

[0127] S3. Reduce the pressure of the pressure clamp to 0.8 N / m, adjust the temperature to room temperature, and then perform constant current charge-discharge cycles at a current density of 0.2C (charging) / 1C (discharging). The charging cut-off voltage is 4.3V and the discharging cut-off voltage is 3.0V.

[0128] Table 1

[0129]

[0130] According to the data in Table 1, the first coulombic efficiency of the electrodeless lithium metal batteries in Examples 1 to 7 after formation is greater than or equal to 94.36%, the number of cycles corresponding to 80% cycle capacity retention is more than 169, and the average coulombic efficiency at the corresponding number of cycles is greater than or equal to 98.22%. This indicates that the formation method of the present invention can significantly improve the cycle performance of electrodeless lithium metal batteries.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for forming a negative electrode-free lithium metal battery, characterized in that, Includes the following steps: S1. Place the battery cell at temperature T0 and let it stand for a time t0. S2. Without applying pressure or temperature T0 to the battery cell, perform pulse charging on the battery cell with a current density I0 for a total duration of t1. S3. Restore the temperature of the battery cell to room temperature; S4. Under pressure P1 and temperature T1, the battery cell is subjected to charge and discharge cycles; S5. Under pressure P2 and temperature of 25°C, the battery cell is subjected to charge and discharge cycles. Among them, -15℃≤T0<25℃, I0≤2.2C, P1≤2.2N / m, P2≤P1, T1≥30℃, 1.0h≤t0≤10.0h, 90s≤t1≤400s.

2. The formation method as described in claim 1, characterized in that, At least one of the following conditions (1) to (7) must be met: （1）-10℃≤T0≤10℃； (2) 2h≤t0≤8h; (3) 0.05C≤I0≤1.5C; (4) 100s≤t1≤350s; (5)1.2N / m≤P1≤1.9N / m; （6）35℃≤T1≤70℃； (7)0.5N / m≤P2≤1.9N / m.

3. The formation method as described in claim 2, characterized in that, At least one of the following conditions (1) to (7) must be met: （1）-5℃≤T0≤5℃； (2) 3h≤t0≤5h; (3) 0.1C≤I0≤1C; (4) 110s≤t1≤300s; (5)1.5N / m≤P1≤1.8N / m; （6）40℃≤T1≤60℃； (7)0.7N / m≤P2≤1.8N / m.

4. The formation method as described in claim 1, characterized in that, Step S4 is as follows: Under pressure P1 and temperature T1, the battery cell is charged with constant current and constant voltage at current density I1 to the first cutoff voltage V1, and the constant voltage charging state of V1 is maintained for time t3; then, the battery cell is charged with constant current and constant voltage at current density I2 to the second cutoff voltage V2, with a cutoff current of 0.01C, and left to stand for 20 to 30 minutes; then, the battery cell is discharged with current density I3 to the cutoff voltage V3, and this charge-discharge cycle is repeated N times.

5. The formation method as described in claim 4, characterized in that, At least one of the following conditions (1) to (8) must be met: (1) 0.05C≤I1≤1C; (2) 3.8V≤V1≤4.1V; (3) 1min≤t3≤30min; (4) 0.01C≤I2≤0.5C; (5) 4.2V≤V2≤4.4V; (6) 0.05C≤I3≤3C; (7) 2.6V≤V3≤3.4V; （8）1≤N≤10。 6. The formation method as described in claim 1, characterized in that, Step S5 specifically involves: under pressure P2 and 25°C, charging the battery cell at a constant current density of 0.1C to 0.33C until the cutoff voltage of 4.3V, and then discharging it at a constant current density of 0.5C to 1C until the cutoff voltage of 3V.

7. The formation method as described in claim 1, characterized in that, In step S2, the pulse interval time of pulse charging is t2, and the pulse charging frequency is f; 1s≤t2≤5s, 1Hz≤f≤50Hz.

8. The formation method as described in claim 1, characterized in that, The battery cell includes a positive electrode, a negative electrode, and an electrolyte; the electrolyte includes a lithium salt and an organic solvent. The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium difluoroborate oxalate. The organic solvent includes at least one of ethylene glycol dimethyl ether, ethylene carbonate, ethyl propionate, vinylene carbonate, fluoroethylene carbonate, diethyl carbonate, 1,3-dioxolane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and tetrahydrofuran.

9. The formation method as described in claim 8, characterized in that, The positive electrode includes a positive electrode active material, which includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium-rich layered materials.

10. The formation method as described in claim 8, characterized in that, The negative electrode includes a negative electrode current collector, which includes any one of copper foil current collector, copper-zinc plated current collector, copper-nickel plated current collector, and copper-silver plated current collector.

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