Current collector, secondary battery, battery module, battery pack, and electrical device

Abstract

The present invention provides a current collector, a secondary battery, a battery module, a battery pack, and an electrical device having a coating. The coating includes at least a surface modification layer, and the coating is formed on at least one side of the current collector, with the surface modification layer having a thickness of 100 nm to 10 μm. The coating formed on at least one side of the current collector effectively blocks direct contact between the negative electrode metal and the electrolyte components, reduces side reactions between the negative electrode metal and the electrolyte, significantly reduces gas generation during battery cycling, and improves the cycle performance and safety of the battery.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application references Chinese patent application No. 202310120204.8, filed on February 15, 2023, entitled "Current Collector, Secondary Battery, Battery Module, Battery Pack and Electrical Device," the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] The present application relates to the technical field of secondary batteries, and in particular to current collectors, secondary batteries, battery modules, battery packs, and electrical devices. [Background technology]

[0003] In recent years, secondary batteries have been widely applied in energy storage power supply systems such as hydroelectric, thermal, wind and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0004] The performance of secondary batteries depends to a large extent on the chemical properties of their interfaces. However, during repeated charge-discharge cycles, side reactions between the electrodes and the electrolyte can deteriorate the chemical properties of the interfaces, resulting in a decrease in the storage performance and capacity fade of the secondary battery, as well as serious safety risks. Summary of the Invention

[0005] The present application has been made in view of the above problems, and its object is to provide a current collector having a coating that reduces gas generation in a battery and improves battery safety.

[0006] A first aspect of the present application provides a current collector having a coating, the coating including at least a surface modification layer, and the coating is formed on at least one side of the current collector, and the thickness of the surface modification layer is 100 nm to 10 μm.

[0007] The surface modification layer blocks direct contact between the negative electrode active material, such as the negative electrode metal, and the electrolyte, reduces the occurrence of side reactions between the metal and the electrolyte, significantly reduces gas generation, effectively reduces the battery expansion rate, and improves the cycle capacity retention rate of the battery.

[0008] In any embodiment, the thickness of the surface modification layer is from 100 nm to 500 nm.

[0009] Controlling the thickness of the surface modification layer between 100 nm and 500 nm ensures that the current collector has good conductivity and consistent mechanical strength, contributing to the transfer of electrons between the various components of the battery and improving the battery's interfacial stability, cycling performance, and safety. If the surface modification layer is too thin, it cannot resist the volume change on the anode side during charging and discharging, resulting in cracking and ineffectiveness, and further recurring gas generation problems due to reactions. If the surface modification layer is too thick, it will inhibit the transfer of metal ions, increase interfacial impedance, and worsen the battery's interfacial polarization, reducing the battery's cycling performance and energy density. A surface modification layer within this thickness range provides a deposition framework for the anode material in anode-free secondary batteries, further improving the electrochemical performance of anode-free batteries.

[0010] In any embodiment, the density of the surface modification layer is 1.7 to 5.5 g / cm 3 and selectively 2.5 to 5.2 g / cm 3 is.

[0011] The density of the surface modification layer is 1.7 to 5.5 g / cm 3 In this case, it is possible to ensure the formation of a uniform and dense surface modification layer on the surface of the current collector, which can provide an effective physical barrier between the electrolyte and the negative electrode metal, prevent side reactions from occurring between the electrolyte and the negative electrode metal, and improve the interface stability, cycle performance, and safety of the battery.

[0012] The density of the surface modification layer is 2.5 to 5.2 g / cm 3In this case, the surface modification layer provides an effective physical shielding effect, forms an effective physical barrier between the electrolyte and the negative electrode metal, prevents side reactions between the electrolyte and the negative electrode metal, and can improve the interfacial stability, cycle performance, and safety of the battery. It can also provide an effective deposition framework, which allows the deposited negative electrode material to be deposited inside the surface modification layer, and further enhances the alloying effect of the metal material and the negative electrode material in the surface modification layer.

[0013] In any embodiment, the surface modification layer comprises one or more of zinc oxide, aluminum oxide, titanium oxide, tin oxide, zirconium oxide, silicon oxide, and antimony oxide.

[0014] Forming a surface modification layer containing one or more of zinc oxide, aluminum oxide, titanium oxide, tin oxide, zirconium oxide, silicon oxide, and antimony oxide on at least one side of the current collector establishes a stable, ionically conductive, and electronically insulating solid electrolyte interface (SEI) on the surface of the current collector, blocking the reaction between the electrolyte and the deposited sodium metal, reducing the gas generated by side reactions between the electrolyte and the deposited sodium metal, and improving the cycle stability and safety of the battery. At the same time, the surface modification layer has good stability and does not react with the electrolyte, further improving the safety of the battery.

[0015] In an optional embodiment, the surface modification layer comprises one or more of tin oxide, antimony oxide.

[0016] An alloying action occurs between the tin oxide and antimony oxide in the surface modification layer and the sodium element deposited on the negative electrode-free secondary battery, further improving the cycle performance of the battery.

[0017] In any embodiment, at 25° C., a 1 mol / L solution of sodium hexafluorophosphate in ethylene glycol dimethyl ether has a contact angle of less than 50° on the current collector having the coating.

[0018] The deposition of the surface modification layer improves the wetting of the electrolyte on the surface of the current collector, reduces interfacial polarization, significantly reduces interfacial impedance, and improves the cycle capacity retention rate of the battery.

[0019] In an optional embodiment, the surface modification layer is fabricated by magnetron sputtering.

[0020] Magnetron sputtering can form a surface modification layer on the current collector surface that combines high mechanical strength and good ionic conductivity. This surface modification layer blocks direct contact between the anode metal and electrolyte components, reducing the amount of gas generated by side reactions between the anode metal and electrolyte, thereby improving battery safety. At the same time, the surface modification layer produced by magnetron sputtering is stable and does not react with the electrolyte, contributing to the uniform deposition of metal ions, improving the interfacial stability of the battery, reducing interfacial impedance, and improving the battery's cycle capacity retention rate.

[0021] In any embodiment, the high frequency power of the magnetron sputtering is 40 to 120 W, and the sputtering time is 30 s to 20 min.

[0022] When the magnetron sputtering is performed with a high frequency power of 40 to 120 W and the sputtering time is 30 seconds to 20 minutes, a uniform, dense, and stable surface modification layer can be formed on the surface of the current collector. This surface modification layer can prevent direct contact between the anode metal and the electrolyte components, reduce the large amount of gas generated by side reactions between the anode metal and the electrolyte, and improve the safety of the battery.

[0023] In any embodiment, the surface modification layer directly contacts the surface of the current collector.

[0024] In any embodiment, the coating further comprises a guided deposition layer, and the guided deposition layer and the surface modification layer are provided in this order from a position closer to the current collector to a position further away from the current collector.

[0025] By sequentially providing the induced deposition layer and the surface modification layer on the current collector, it is possible to reduce the nucleation overpotential of metal ions, induce the metal ions to be deposited uniformly, adjust the deposition behavior of metal ions, and inhibit dendrites, as well as to reduce contact between the metal and the electrolyte and reduce the occurrence of side reactions between the metal and the electrolyte, thereby effectively improving the safety and cycle capacity retention rate of the battery.

[0026] In any embodiment, the guided deposition layer comprises a carbon material.

[0027] The induced deposition layer containing the carbon material reduces the nucleation overpotential of metal ions and contributes to increasing the coulombic efficiency and cycle capacity retention of the battery.

[0028] In any embodiment, the current collector comprises at least one of a metal foil, a metal foam current collector, and a metal mesh current collector.

[0029] The current collector has excellent tensile strength and ductility, which contributes to the stability and safety of the battery.

[0030] A second aspect of the present application provides a secondary battery including a negative electrode plate, the negative electrode plate including the current collector in any embodiment.

[0031] This secondary battery has excellent cycle performance.

[0032] In any embodiment, the secondary battery is a sodium secondary battery.

[0033] In any embodiment, the secondary battery is a negative electrode-free sodium secondary battery, which can have a high energy density.

[0034] In any embodiment, the secondary battery includes a positive electrode plate, and the ratio of the thickness of the surface modification layer to the amount of positive electrode active material carried per unit area of ​​the positive electrode plate is 50 to 500 nm cm 2 / mAh.

[0035] The ratio of the thickness of the surface modification layer to the amount of positive electrode active material carried per unit area of ​​the positive electrode plate is 50 to 500 nm cm 2 / mAh, the surface modification layer can ensure good ionic conductivity, electron blocking ability, and high mechanical strength, reducing side reactions between the electrode metal and the electrolyte and improving the safety of the battery. Furthermore, the surface modification layer can effectively block solvation molecules from penetrating the surface of the negative electrode and has good ion transfer ability, ensuring that desolvated metal ions can quickly pass through this layer to reach the surface of the negative electrode and receive electrons to be reduced to metal, improving the cycle performance of the battery. Meanwhile, the surface modification layer has good mechanical strength, can withstand the volume change of the negative electrode metal during charging and discharging, and will not crack or become ineffective, thereby preventing the recurrence of gas generation problems due to reactions and ensuring the safety of the battery during high temperature or long cycles.

[0036] In any embodiment, the secondary battery includes an electrolyte solution, the electrolyte solution including a sodium salt, the sodium salt including one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide.

[0037] In any embodiment, after the secondary battery has been subjected to 50 charge-discharge cycles, the total mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte is less than 0.0001%, based on the total mass of the electrolyte.

[0038] After 50 charge-discharge cycles of the secondary battery, it was confirmed that when the total mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte was less than 0.0001% based on the total mass of the electrolyte, the surface modification layer had good electrochemical stability and did not react with the electrolyte during the charge-discharge cycle, nor did it dissolve in the electrolyte and fall off from the surface of the current collector. Therefore, the surface modification layer effectively blocks reactions between the electrolyte and the deposited metals, improving the cycle stability and safety of the battery.

[0039] A third aspect of the present application provides a battery module including the secondary battery according to the second aspect of the present application.

[0040] A fourth aspect of the present application provides a battery pack including the secondary battery according to the second aspect of the present application or the battery module according to the third aspect of the present application.

[0041] A fifth aspect of the present application provides an electric device including at least one of the secondary battery according to the second aspect of the present application, the battery module according to the third aspect of the present application, and the battery pack according to the fourth aspect of the present application. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application. [Figure 6] 1 is a schematic diagram of an electrical device that uses a secondary battery as a power source according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the current collector, secondary battery, battery module, battery pack, and electric device of the present application will be described in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate easy understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the scope of the claims.

[0044] The "ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits are specific The boundaries of a range are defined. Such defined ranges may be inclusive or exclusive and may be arbitrarily combined; i.e., any lower limit can be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a given parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are recited as the minimum range values ​​and 3, 4, and 5 are recited as the maximum range values, then the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. Unless otherwise specified herein, a numerical range "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range "0 to 5" means that all real numbers between "0 and 5" are recited herein, and "0 to 5" is simply a shorthand notation for these combinations of numbers. It should be noted that describing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise stated, all embodiments and alternative embodiments in the present application can be combined with each other to form new technical solutions.

[0046] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0047] Unless otherwise specified, all steps herein may be performed in sequence or randomly, preferably in sequence. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

[0048] Unless otherwise specified, the terms "comprise" and "comprises" used herein may be open-ended or closed-ended. For example, the terms "comprise" and "comprises" may indicate that the compound may further include or include other components not listed, or may include or include only the listed components.

[0049] Unless otherwise stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0050] Metal secondary batteries are secondary batteries that use a metal material (e.g., lithium, sodium, magnesium, potassium, etc.) as the negative electrode. The metal material on the negative electrode current collector can be pre-deposited on the surface of the current collector as the negative electrode active material, or it can be deposited in situ on the surface of the current collector during the charge and discharge process. That is, metal secondary batteries include not only sodium batteries, lithium batteries, magnesium batteries, potassium batteries, etc., which have a negative electrode active material, but also anode-free secondary batteries. In anode-free secondary batteries, the negative electrode plate is a negative electrode current collector, and no anode active material is pre-deposited. Instead, metal ions are deposited in situ on the anode current collector during the initial charge and discharge process. The solid electrolyte interphase (SEI), formed by the chemical and electrochemical reaction between the metal anode and the electrolyte, is a key factor in determining the long-term stability of the battery. However, during repeated charge-discharge cycles, the SEI formed on the surface of the metal anode becomes unstable due to volume changes in the metal anode, and some components are easily dissolved in the electrolyte. This causes side reactions when the exposed metal directly contacts the electrolyte, and the gas generated by the side reactions accumulates during cycling and storage, resulting in a decrease in capacity and serious safety issues.

[0051] [Current collector] Based on this, the present application provides a current collector having a coating, the coating including at least a surface modification layer, and the coating is formed on at least one side of the current collector, and the thickness of the surface modification layer is 100 nm to 10 μm.

[0052] In some embodiments, the coating does not directly contact the current collector, and other layers are included between the coating and the current collector, including, but not limited to, a negative electrode active material layer.

[0053] In some embodiments, the current collector having the coating functions as a negative electrode current collector in a secondary battery.

[0054] In some embodiments, the coating is located on a surface of a current collector, and the current collector having the coating is used directly as a negative electrode current collector in a negative electrode-free secondary battery.

[0055] In some embodiments, the term "surface modification layer" refers to a layer formed by a physical or chemical method that modifies the surface state of the current collector.

[0056] In some embodiments, the coating further comprises an optional layer other than the surface modification layer, including but not limited to a guided deposition layer, and the synergistic effect between each layer further improves the cycling stability of secondary batteries, particularly anode-free secondary batteries.

[0057] The surface modification layer blocks direct contact between the negative electrode active material, such as the negative electrode metal, and the electrolyte, reduces the occurrence of side reactions between the metal and the electrolyte, significantly reduces gas generation, effectively reduces the battery expansion rate, and improves the cycle capacity retention rate of the battery.

[0058] In some embodiments, the thickness of the surface modification layer is from 100 nm to 10 μm.

[0059] In some embodiments, the thickness of the surface modification layer is optionally 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 310 nm, 320 nm, 330 nm, 340 nm, 350 nm, 360 nm, 370 nm, 380 nm, 390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, 460 nm, 470 nm, 480 nm, 490 nm, 500 nm, 510 nm, 520 nm, 530 nm, 540 nm, 550 nm, 560 nm, 570 nm, 580 nm, 590 nm, 600 nm, 610 nm, 620 nm, 630 nm, 640 nm, 650 nm, 660 nm, 670 nm, 680 nm, 690 nm, 700 nm, 710 nm, 720 nm, 730 nm, 740 nm, 750 nm, 760 nm, 770 nm, 780 nm, 790 nm, 800 nm, 810 nm, 820 nm, 830 nm, 840 nm, 850 nm, 860 nm, 870 nm, 880 nm, 890 nm, 900 nm, 910 nm, 920 nm, nm, 570nm, 580nm, 590nm, 600nm, 610nm, 620nm, 630nm, 640nm, 650nm, 660nm, 670nm, 680nm, 6 90nm, 700nm, 710nm, 720nm, 730nm, 740nm, 750nm, 760nm, 770nm, 780nm, 790nm, 800nm, 810nm, 820nm, 830nm, 840nm, 850nm, 860nm, 870nm, 880nm, 890nm, 900nm, 910nm, 920nm, 930nm, 940nm, 950nm, 960nm, 970nm, 980nm, 990nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0060] Controlling the thickness of the surface modification layer between 100 nm and 10 μm ensures that the current collector has good conductivity and consistent mechanical strength, contributing to the transfer of electrons between the battery components and improving the battery's interface stability, cycle performance, and safety. If the surface modification layer is too thin, it cannot resist the volume change on the anode side during charging and discharging, resulting in cracking and ineffectiveness, and further causing gas generation problems due to reactions. If the surface modification layer is too thick, it will inhibit the transfer of metal ions, increase interfacial impedance, and worsen the battery's interfacial polarization, reducing the battery's cycle performance and energy density.

[0061] In some embodiments, the thickness of the surface modification layer is 100 nm to 500 nm.

[0062] Controlling the thickness of the surface modification layer between 100 nm and 500 nm ensures that the current collector has good conductivity and consistent mechanical strength, contributing to the transfer of electrons between the various components of the battery and improving the battery's interfacial stability, cycling performance, and safety. If the surface modification layer is too thin, it cannot resist the volume change on the anode side during charging and discharging, resulting in cracking and ineffectiveness, and further recurring gas generation problems due to reactions. If the surface modification layer is too thick, it will inhibit the transfer of metal ions, increase interfacial impedance, and worsen the battery's interfacial polarization, reducing the battery's cycling performance and energy density. A surface modification layer within this thickness range provides a deposition framework for the anode material in anode-free secondary batteries, further improving the electrochemical performance of anode-free batteries.

[0063] In some embodiments, the density of the surface modification layer is 1.7 to 5.5 g / cm 3 and selectively 3.5 to 5.2 g / cm 3 is.

[0064] In some embodiments, the density of the surface modification layer is 1.7 g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 , 3.1g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 , 3.4g / cm 3 , 3.5g / cm 3 , 3.6g / cm 3 , 3.7g / cm 3, 3.8g / cm 3 , 3.9g / cm 3 , 4.0g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 , 4.4g / cm 3 , 4.5g / cm 3 , 4.6g / cm 3 , 4.7g / cm 3 , 4.8g / cm 3 , 4.9g / cm 3 , 5.0g / cm 3 , 5.1g / cm 3 , 5.2g / cm 3 , 5.3g / cm 3 , 5.4g / cm 3 or 5.5g / cm 3 is.

[0065] The density of the surface modification layer is 1.7 to 5.5 g / cm 3 In this case, it is possible to ensure that a uniform and dense surface modification layer is formed on the surface of the current collector, which forms a physical barrier between the electrolyte and the negative electrode metal, prevents side reactions from occurring between the electrolyte and the negative electrode metal, and improves the interface stability, cycle performance, and safety of the battery.

[0066] The density of the surface modification layer is 2.5 to 5.2 g / cm 3 In this case, the surface modification layer not only provides an effective physical shielding effect, forms an effective physical barrier between the electrolyte and the negative electrode metal, prevents side reactions between the electrolyte and the negative electrode metal, and improves the interfacial stability, cycle performance, and safety of the battery, but also provides an effective deposition framework, thereby generating an effective alloying effect between the surface modification layer and the deposited negative electrode material.

[0067] In some embodiments, the surface modification layer comprises one or more of zinc oxide (ZnO), aluminum oxide (Al2O3), titanium oxide (TiO2), tin oxide (SnO2), zirconium oxide (ZrO2), silicon oxide (SiO2), antimony oxide (Sb2O3 / Sb2O5).

[0068] Forming a surface modification layer containing one or more of zinc oxide, aluminum oxide, titanium oxide, tin oxide, zirconium oxide, silicon oxide, and antimony oxide on at least one side of the current collector establishes a stable, ionically conductive, and electronically insulating solid electrolyte interface (SEI) on the surface of the current collector, blocking the reaction between the electrolyte and the deposited sodium metal, reducing the gas generated by side reactions between the electrolyte and the deposited sodium metal, and improving the cycle stability and safety of the battery. At the same time, the surface modification layer has good stability and does not react with the electrolyte, further improving the safety of the battery.

[0069] In some embodiments, the surface modification layer comprises one or more of tin oxide, antimony oxide.

[0070] The alloying action occurs between tin oxide, antimony oxide and elemental sodium deposited in the anode-free secondary battery, forming a tin-sodium alloy or an antimony-sodium alloy, which further improves the cycle performance of the battery. At the same time, the presence of tin oxide and antimony oxide can reduce the nucleation overpotential of elemental sodium, improve the deposition uniformity of elemental sodium in the anode-free secondary battery, and improve the overall performance of the battery.

[0071] As used herein, the term "nucleation overpotential" refers to the additional potential required for the nucleation of a metal ion, or the value by which a metal ion is offset from its corresponding deposition-detachment potential, which is derived from the critical nucleation radius of the metal ion. In some embodiments, at 25°C, a 1 mol / L solution of sodium hexafluorophosphate in ethylene glycol dimethyl ether has a contact angle of less than 50° on a current collector having a coating.

[0072] The deposition of the surface modification layer improves the wetting of the electrolyte on the surface of the current collector, reduces interfacial polarization, increases the wetting of the electrolyte into the negative electrode, and improves the dynamic performance and cycle performance of the battery.

[0073] In some embodiments, the surface modification layer is fabricated by magnetron sputtering.

[0074] Magnetron sputtering is a physical vapor deposition method that introduces a magnetic field onto the surface of a target cathode, increasing the plasma density to increase the sputtering rate by constraining charged particles in the magnetic field. Compared to surface modification layers deposited by other physical vapor deposition methods, the surface modification layer deposited by magnetron sputtering exhibits an alloying effect with the negative electrode active material deposited on the negative electrode during the charge and discharge process, thereby improving the cycle performance of secondary batteries.

[0075] Magnetron sputtering can form a surface modification layer on the current collector surface that combines high mechanical strength and good ionic conductivity. This surface modification layer blocks direct contact between the anode metal and electrolyte components, reducing the amount of gas generated by side reactions between the anode metal and electrolyte, thereby improving battery safety. At the same time, the surface modification layer produced by magnetron sputtering is stable and does not react with the electrolyte, contributing to the uniform deposition of metal ions, improving the interfacial stability of the battery, reducing interfacial impedance, and improving the battery's cycle capacity retention rate.

[0076] The thickness or density of the magnetron sputtered deposition layer can be adjusted by varying the magnetron sputtering process parameters. In some embodiments, the thickness or density of the magnetron sputtered layer is adjusted by varying any of the magnetron sputtering parameters, such as the RF power, sputtering pressure, deposition rate, and sputtering time. In some embodiments, if the magnetron sputtering parameters are not changed, the thickness of the magnetron sputtered layer increases and the density decreases as the sputtering time increases, resulting in larger voids in the magnetron sputtered layer and a smaller contact angle of the electrolyte thereon.

[0077] In some embodiments, the high frequency power of the magnetron sputtering is 40 to 120 W, and the sputtering time is 30 seconds to 60 minutes.

[0078] In some embodiments, the RF power of the magnetron sputtering is optionally 40W, 45W, 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, 95W, 100W, 105W, 110W, 115W, or 120W, and the sputtering time is optionally 30s, 35s, 40s, 45s, 50s, 55s, 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0079] When the magnetron sputtering is performed with a high frequency power of 40 to 120 W and the sputtering time is 30 seconds to 20 minutes, a uniform, dense, and stable surface modification layer can be formed on the surface of the current collector. This surface modification layer can prevent direct contact between the anode metal and the electrolyte components, reduce the large amount of gas generated by side reactions between the anode metal and the electrolyte, and improve the safety of the battery.

[0080] In some embodiments, the surface modification layer directly contacts the surface of the current collector.

[0081] In some embodiments, the coating further comprises a guided deposition layer, and the guided deposition layer and the surface modification layer are provided in this order from closer to the current collector to further away from the current collector.

[0082] In this specification, the guided deposition layer provides a sufficient number of nucleation sites to guide the metal to be deposited uniformly and to help suppress metal dendrites.

[0083] In some embodiments, the guided deposition layer comprises a carbon material.

[0084] The induced deposition layer containing the carbon material reduces the nucleation overpotential of metal ions and contributes to increasing the coulombic efficiency and cycle capacity retention of the battery.

[0085] As used herein, the term "carbon material" refers to a material containing carbon. By way of example, carbon materials include, but are not limited to, Super P, carbon nanotubes, hard carbon, two-dimensional graphene, or graphene quantum dots.

[0086] As used herein, the term "Super P" refers to carbon black in which particles are aggregated to form spheres.

[0087] As used herein, the term "carbon nanotube" refers to a seamless hollow cylinder formed by rolling single- or multi-walled graphene, with a tube diameter of less than 100 nm and a tube length of more than 100 nm. By way of example, carbon nanotubes include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0088] As used herein, the term "hard carbon" refers to carbon that is difficult to graphitize.

[0089] In some embodiments, two-dimensional graphene refers to a sheet-like structure of graphene that is nanoscale (less than 100 nm) in size in the thickness direction and greater than 100 nm in size in other directions, and can include single-layer graphene and / or multi-layer graphene.

[0090] As used herein, the term "single-layer graphene" refers to a single-layer sheet-like structure in which carbon atoms are densely and periodically arranged in a hexagonal honeycomb structure. For example, the thickness of single-layer graphene is only 0.3 nm to 0.4 nm.

[0091] In this specification, the term "multilayer graphene" refers to a graphene produced by stacking 2 to 10 single-layer graphene layers, the total thickness of which is less than 100 nm.

[0092] As used herein, the term "graphene quantum dots" refers to graphene nanoparticles whose graphene size is within 100 nm in all dimensions.

[0093] In some embodiments, the current collector comprises at least one of a metal foil, a metal foam current collector, and a metal mesh current collector.

[0094] In some embodiments, the metal foil is optionally copper foil, aluminum foil, stainless steel foil, iron foil, zinc foil, titanium foil, and the metal foam current collector is optionally copper foam, aluminum foam, zinc foam, etc. The metal mesh current collector is optionally copper mesh, aluminum mesh, etc.

[0095] The current collector has excellent tensile strength and ductility, which contributes to the stability and safety of the battery. [Secondary battery]

[0096] One embodiment of the present application provides a secondary battery, the secondary battery including a negative electrode plate, the negative electrode plate including a current collector in some embodiments.

[0097] In some embodiments, the secondary battery is a sodium secondary battery.

[0098] In some embodiments, the secondary battery is an anode-free sodium secondary battery. Anode-free sodium secondary batteries do not use an anode active material, but instead use only an anode current collector as the anode. Sodium is plated onto the anode during the initial charge process, and then returned to the cathode during discharge, achieving a charge-discharge cycle. Because anode-free batteries use only an anode current collector and no anode material, they effectively overcome the deficiencies of sodium metal batteries and can achieve a higher energy density than metallic sodium anodes. Furthermore, because anode-free secondary batteries do not have an anode active material, they ensure high electrochemical performance while also reducing the battery manufacturing cycle and cost and optimizing battery manufacturing efficiency.

[0099] In some embodiments, the CB value of the negative electrode-free sodium secondary battery is 0.1 or less. The CB value is calculated by dividing the capacity per unit area of ​​the negative electrode plate in the sodium secondary battery by the capacity per unit area of ​​the positive electrode plate. Because the negative electrode-free sodium battery does not contain a negative electrode active material, the capacity per unit area of ​​the negative electrode plate is small, and the CB value of the sodium secondary battery is 0.1 or less.

[0100] The surface modification layer on the negative electrode current collector of the anode-free sodium secondary battery functions as an artificial SEI layer, blocking side reactions between the electrolyte and the deposited sodium metal, regulating the uniform deposition of metal ions, suppressing the growth of dendrites, and maintaining the overall stability of the metal anode during cycling. Furthermore, the artificial SEI layer has good mechanical strength, can withstand the volume expansion of the anode under different loads, and can significantly reduce gas generation during long-term battery cycling, further improving the safety of the battery.

[0101] In some embodiments, the secondary battery includes a positive electrode plate.

[0102] In some embodiments, the ratio of the thickness of the surface modification layer to the amount of positive electrode active material supported per unit area of ​​the positive electrode plate is 50 to 500 nm cm 2 / mAh.

[0103] The thickness per unit area capacity of the surface modification layer = thickness of the surface modification layer / (theoretical gram capacity of the positive electrode active material x area density of the positive electrode active material).

[0104] In some embodiments, the thickness per unit area of ​​the surface modification layer is preferably 50 nm cm 2 / mAh, 100nm·cm 2 / mAh, 150nm·cm 2 / mAh, 200nm·cm 2 / mAh, 250nm·cm 2 / mAh, 300nm·cm 2 / mAh, 350nm·cm 2 / mAh, 400nm·cm2 / mAh, 450nm·cm 2 / mAh, 500nm·cm 2 / mAh. The thickness of the surface modification layer can be adjusted according to the unit area capacity of the positive electrode active material so that the thickness of the surface modification layer can be adapted to different types / loading amounts of positive electrode active material. The ratio of the thickness of the surface modification layer to the amount of positive electrode active material loaded per unit area of ​​the positive electrode plate is 50 to 500 nm cm 2 / mAh, the surface modification layer can ensure good ionic conductivity, electron blocking ability, and high mechanical strength, reducing side reactions between the electrode metal and the electrolyte and improving the safety of the battery. Furthermore, the surface modification layer can effectively block solvation molecules from penetrating the surface of the negative electrode and has good ion transfer ability, ensuring that desolvated metal ions can quickly pass through this layer to reach the surface of the negative electrode and receive electrons to be reduced to metal, improving the cycle performance of the battery. Meanwhile, the surface modification layer has good mechanical strength, can withstand the volume change of the negative electrode metal during charging and discharging, and will not crack or become ineffective, thereby preventing the recurrence of gas generation problems due to reactions and ensuring the safety of the battery during high temperature or long cycles.

[0105] In some embodiments, the positive electrode plate further includes a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, and the positive electrode active material may include one or more of a Prussian blue compound, a polyanion-type compound, and a layered transition metal oxide.

[0106] The transition metal in the layered transition metal oxide may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Optionally, the layered transition metal oxide may be, for example, Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu; <x≦1である。

[0107] Polyanionic compounds include metal ions, transition metal ions, and tetrahedral (YO4) nThe compound may have an anionic unit, wherein the metal ion is optionally one of sodium ion, lithium ion, potassium ion, and zinc ion, the transition metal is optionally at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y is optionally at least one of P, S, and Si, and n is (YO4) n represents the valence of the atom.

[0108] The Prussian blue compound may be a compound having a sodium ion, a transition metal ion, and a cyanide ion (CN). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound may be, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn; <a≦2、0<b<1、0<c<1である。

[0109] The positive electrode active material layer may further include a conductive agent to improve the conductive performance of the positive electrode, which may be one or more of Super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0110] The positive electrode active material layer may further include a binder to firmly bond the positive electrode active material and optional conductive agent to the positive electrode current collector, and the binder may optionally be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyethylene alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMCS).

[0111] In some embodiments, the surfaces of the positive electrode active material particles have a coating layer, and the coating layer includes one or more of a carbon material, polyaniline (PANI), polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT), aluminum oxide (AlO), zinc oxide (ZnO), titanium oxide (TiO), zirconium oxide (ZrO), magnesium oxide (MgO), silicon oxide (SiO), lanthanum oxide (LaO), sodium fluoride (NaF), lithium fluoride (LiF), and aluminum fluoride (AlF), and the carbon material includes one or more of amorphous carbon, graphite, and graphene.

[0112] The coating layer effectively improves the stability of the positive electrode active material, reduces the metal elution and particle crushing during cycling of the positive electrode active material, and effectively improves the cycle performance and storage stability of the battery.

[0113] In some embodiments, the thickness of the coating layer is between 2 nm and 1000 nm, and optionally between 10 nm and 100 nm.

[0114] In some embodiments, the thickness of the coating layer is optionally 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm.

[0115] A coating layer with an appropriate thickness can effectively improve the performance, and can avoid the problem of the coating layer being too thick, which would result in the diaphragm resistance of the positive electrode becoming too high and causing a decrease in battery performance.

[0116] In some embodiments, a positive electrode plate can be manufactured by the following method. The components for manufacturing the positive electrode plate described above, such as the positive electrode active material, conductive agent, binder, and any other optional components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is applied to a positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode plate can be obtained.

[0117] In some embodiments, the secondary battery further comprises an electrolyte.

[0118] The electrolyte serves to conduct ions between the positive and negative electrodes. In this application, the type of electrolyte is not specifically limited and can be selected according to needs. For example, the electrolyte may be liquid, gel-like, or all solid.

[0119] In some embodiments, the electrolyte is an electrolytic solution, which includes a sodium salt and a solvent.

[0120] In some embodiments, the sodium salt comprises one or more of sodium perchlorate (NaClO), sodium tetrafluoroborate (NaBF), sodium hexafluorophosphate (NaPF), sodium hexafluoroarsenate (NaAsF), sodium trifluoroacetate (CFCOONa), sodium tetraphenylborate (NaB(CH)), sodium trifluoromethanesulfonate (NaSOCF), sodium bis(fluorosulfonyl)imide (Na[(FSO)N]), sodium bis(trifluoromethanesulfonyl)imide (Na[(CFSO)N]).

[0121] In some embodiments, the solvent comprises one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), 1,3-dioxolane (DOL), ethylene glycol diethyl ether (DEE), diethylene glycol diethyl ether (DEGDEE), diisopropyl ether (DIE), dibutyl ether (DBE), diethylene glycol dibutyl ether (DEGDBE), 1,4-dimethoxybutane (DMB), 1,4-diethoxybutane (DEB), tetrahydrofuran (THF), 15-crown-5, 12-crown-4, and 18-crown-6.

[0122] The molecules of the ether solvent can establish a stable electrode / electrolyte interface on the surface of the negative electrode, forming a stable solid electrolyte interface (SEI), reducing electrochemical polarization and improving the battery's coulombic efficiency and cycle capacity retention rate.

[0123] Taking the example of an anode-free sodium metal battery, ether-based solvents have high compatibility with sodium metal anodes, can effectively passivate sodium metal, form a thin, uniform and dense SEI film on the surface of the sodium metal, and further inhibit the formation of sodium dendrites, preventing the SEI film from becoming thicker due to the growth and evolution of sodium dendrites, which would affect ion conduction.

[0124] In some embodiments, the electrolyte solution optionally further contains additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving a specific performance of the battery, such as an additive for improving the overcharge performance of the battery, or an additive for improving the high-temperature or low-temperature performance of the battery.

[0125] In some embodiments, after the secondary battery has been subjected to 50 charge-discharge cycles, the total mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte is less than 0.0001%, based on the total mass of the electrolyte.

[0126] After 50 charge-discharge cycles of the secondary battery, it was confirmed that when the total mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte was less than 0.0001% based on the total mass of the electrolyte, the surface modification layer had good electrochemical stability and did not react with the electrolyte during the charge-discharge cycle, nor did it dissolve in the electrolyte and fall off from the surface of the current collector. Therefore, the surface modification layer effectively blocks reactions between the electrolyte and the deposited metals, improving the cycle stability and safety of the battery.

[0127] In some embodiments, the secondary battery further includes a separator. In the present application, the type of separator is not particularly limited, and any separator with a known porous structure having good chemical stability and mechanical stability can be selected.

[0128] In some embodiments, the separator may be made of at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid fiber, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0129] In some embodiments, the positive and negative electrode plates and separators can be manufactured into an electrode assembly by a winding or lamination process.

[0130] In some embodiments, the secondary battery may include an exterior body that can be used to package the electrode assembly and the electrolyte.

[0131] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The exterior of the secondary battery may be a soft pack, such as a bag-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0132] In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0133] In some embodiments, referring to FIG. 2 , the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates are enclosed to form a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 may cover the opening to seal the storage chamber. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the storage chamber. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the lithium-ion battery 5 may be one or more, and can be selected by those skilled in the art according to specific actual needs.

[0134] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0135] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fastening members.

[0136] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0137] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0138] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box may include an upper box 2 and a lower box 3, and the upper box 2 may cover the lower box 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0139] The present application also provides an electric device including at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., secondary battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric cars, ships and satellites, energy storage systems, etc.

[0140] For electrical devices, a secondary battery, a battery module, or a battery pack can be selected according to the needs of the device.

[0141] 6 shows an example of an electric device, such as a secondary battery electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements for the secondary batteries of the electric device, a battery pack or a battery module can be adopted.

[0142] Other example devices may be mobile phones, tablets, laptops, etc. Such devices typically require light weight and thinness, and can employ secondary batteries as their power source.

[0143] Example Examples of the present application are described below. The examples described below are illustrative and are intended merely to interpret the present application and should not be understood as limiting the present application. If specific techniques or conditions are not specified in the examples, they are performed according to the techniques or conditions described in literature in the field or according to the product specifications. If the manufacturer of the reagents or equipment used is not specified, they are all ordinary commercially available products. In the following examples, only the case where the secondary battery is a sodium ion battery is shown, but the present application is not limited thereto.

[0144] 1. Manufacturing method Example 1 1) Manufacturing of negative electrode current collector A 100 nm thick tin oxide surface modification layer was deposited on the copper foil surface by magnetron sputtering. The parameters for magnetron sputtering were a high-frequency power of 80 W, a sputtering time of 15 min, and a target-to-substrate distance of 15 cm.

[0145] 2) Manufacturing of positive electrode plates The positive electrode active material Na3V2(PO4)3, the binder polyvinylidene fluoride (PVDF), and the conductive carbon black (Super-P) were uniformly mixed in a mass ratio of 96%:2%:2% in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This was then coated on the surface of aluminum foil using an extrusion coater according to the mass requirement per unit area of ​​the positive electrode active material, baked, and further pressed into a cold press to form a coated electrode plate at a density of 2.5 g / cm. 3 The final positive electrode plate was manufactured by compressing and cold pressing the design.

[0146] 3) Separator A polyethylene film (PE insulating film) was used as the separator.

[0147] 4) Electrolyte production In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the sodium salt sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent ethylene glycol dimethyl ether (DME), and the concentration of NaPF6 was 1 mol / L.

[0148] 5) Manufacturing of anode-free all-batteries The positive electrode plate, separator, and negative electrode current collector were stacked in this order, with the separator positioned between the positive and negative electrode current collectors to provide insulation, and then wound up to obtain a bare cell. A tab was welded to the bare cell, and the bare cell was then packed into an aluminum case and baked at 80°C to remove moisture. The case was then immediately filled with electrolyte and sealed to obtain an uncharged battery. The uncharged battery was then allowed to stand, hot pressed, cold pressed, formed, shaped, and capacity tested to obtain the anode-free sodium metal battery product of Example 1.

[0149] The manufacturing methods of other examples and comparative examples are similar to that of Example 1, and the specific parameters are adjusted as shown in Table 1. By increasing the sputtering time of magnetron sputtering, the thickness of the magnetron sputtering layer is increased. As the magnetron sputtering time increases, the thickness of the magnetron sputtering layer increases, the voids become larger, and its density also decreases to a certain extent, and the contact angle of the electrolyte on the magnetron sputtering layer decreases.

[0150] In Example 9, carbon nanotubes and sodium alginate were added to water and stirred to form a uniform slurry. The slurry was applied to a negative electrode current collector and baked to obtain a negative electrode current collector coated with a carbon nanotube undercoat layer. A sputtering layer was then deposited on the current collector, and the surface density of the undercoat layer was 20 g / m. 2 It was.

[0151] In Example 14, the surface modification layer was deposited on the negative electrode current collector by vapor deposition.

[0152] In Comparative Examples 1 to 3, the negative electrode plate did not have a surface modification layer.

[0153] 2. Performance test 1. Performance test of current collector 1) Thickness test of surface modification layer The thickness d of the surface modification layer was tested using a step gauge.

[0154] 2) Density test of the surface modification layer The weight difference Δm of the current collector before and after modification was measured and recorded using an analytical balance, and the thickness d of the surface modification layer was measured using a step gauge. The area of ​​the modification layer on the current collector surface was S, and the density of the surface modification layer = Δm / (S d).

[0155] 3) Contact angle test For the contact angle test, a dynamic contact angle measuring device (Dataphysics OCV20, Germany) was used, and a 1 mol / L solution prepared by dissolving sodium hexafluorophosphate in ethylene glycol dimethyl ether at 25°C was dropped onto the coated current collector, and the contact angle value was read.

[0156] 2. Battery performance test 1) Trace element analysis of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte after 50 battery cycles After 50 charge-discharge cycles, the battery was disassembled and the electrolyte content was tested using inductively coupled plasma optical emission spectroscopy. The cycle test method was the same as the cycle capacity retention test. Here, the battery refers to the battery after capacity formation. The cycle number of the battery can be directly read from the corresponding software.

[0157] 2) Expansion rate At room temperature (25°C), the battery was charged at a constant current of 0.5C to 4V (layered oxide cathode) or 3.7V (sodium vanadium phosphate cathode). After the battery was fully charged, the initial volume of the battery was measured using the drainage method. The battery was stored at room temperature for 24 days and then removed. The volume of the battery was measured using the drainage method at room temperature. The volume expansion rate of the battery was calculated using the volume of the battery tested before storage. The volume expansion rate (%) of the battery after 24 days of storage at 25°C = (volume of battery measured after storage / volume of battery measured before storage) - 1.

[0158] 3) Cycle capacity retention rate At 25°C and atmospheric pressure (0.1 MPa), the battery was charged at a constant current of 0.5 C until the voltage reached 4 V (layered oxide cathode) or 3.5 V (sodium vanadium phosphate cathode), and then discharged at a constant current of 1 C until the voltage reached 2.4 V (layered oxide cathode) or 3.2 V (sodium vanadium phosphate cathode), which constituted one charge-discharge cycle. The capacity of the first discharge was taken as 100%, and the charge-discharge cycle was repeated. The test was then stopped and the cycle capacity retention rate was recorded. The room temperature capacity retention rate was used as an evaluation index for the room temperature cycle performance of the battery.

[0159] 4) Interface impedance test The resistance test was performed using conventional electrochemical impedance spectroscopy. A voltage perturbation was selected with an amplitude of 5 mV and a frequency of 100 kHz to 0.01 Hz. The Nyquist diagram obtained by the test was subjected to fitting analysis using Zview software to obtain the interfacial impedance value.

[0160] 5) Nucleation overpotential test During the overpotential test, the surface-modified current collector was assembled into a button cell against a sodium sheet at 25°C and subjected to a current of 0.1 mA / cm 2 The discharge was carried out at a constant surface current of 0.05V for 10 hours, and the most negative potential obtained during this process was recorded as the nucleation overpotential.

[0161] 6) Areal capacity of the positive electrode active material The theoretical gram capacity of the positive electrode active material was multiplied by the areal density of the positive electrode active material on the positive electrode plate to obtain the areal capacity of the positive electrode active material.

[0162] 3. Analysis of the test results of each example and comparative example Batteries of each example and comparative example were manufactured by the above method, and performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0163] [Table 1-1] [Table 1-2] [Table 1-3]

[0164] [Table 2]

[0165] As can be seen from the above results, the current collectors of Examples 1 to 14 have a coating, which includes at least a surface modification layer, and the coating is formed on at least one side of the current collector, with a thickness of 100 nm to 10 μm. As can be seen from Examples 1 to 14, a surface modification layer is formed on one side of the negative electrode current collector as a coating on the current collector, and the surface modification layer blocks direct contact between sodium metal and the electrolyte, reducing side reactions between sodium metal and the electrolyte, significantly reducing gas generated by side reactions during long battery cycles, thereby improving battery safety.

[0166] As can be seen from a comparison between Examples 1 to 5 and 7 to 9 and Comparative Example 1, when the thickness of the surface modification layer is 100 nm to 500 nm, the interfacial impedance of the battery can be further reduced and the cycle capacity retention rate of the battery can be increased.

[0167] As can be seen from the comparison between the examples and the comparative examples, at 25°C, a 1 mol / L solution of sodium hexafluorophosphate in ethylene glycol dimethyl ether has a contact angle of less than 50° on the current collector having a magnetron sputtering layer, and the presence of the magnetron sputtering layer significantly increases the surface wettability of the negative electrode current collector, which helps to improve the dynamic performance of the battery.

[0168] As can be seen from a comparison between Examples 1 to 11 and Comparative Example 1, tin oxide and antimony oxide can more effectively reduce the interfacial impedance of a negative electrode-free battery than aluminum oxide, thereby improving the safety performance of the battery and further improving the electrochemical performance of the battery.

[0169] As can be seen from the comparison between Example 1 and Example 14, compared with the surface modification layer deposited by evaporation, the surface modification layer deposited by magnetron sputtering can further improve the battery's expansion resistance, and can provide the battery with lower interfacial impedance and better cycle capacity retention.

[0170] As can be seen from Examples 1 to 14, the anode-free sodium batteries provided by the present application all include anode current collectors with a surface modification layer, and after 50 charge-discharge cycles of the anode-free sodium batteries, the total mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte was <0.0001% based on the total mass of the electrolyte, indicating that the surface modification layer has good stability, is not easily detached during the cycles, and is not easily reacted with the electrolyte.

[0171] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and all embodiments that have substantially the same configuration as the technical idea and exhibit the same functions and effects within the scope of the technical solution of the present application are encompassed within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art can make to the embodiments and other forms constructed by combining some of the components of the embodiments are also encompassed within the scope of the present application, as long as they do not deviate from the gist of the present application. [Explanation of symbols]

[0172] 1 battery pack 2 Upper Box 3 Lower Box 4 Battery Module 5 Secondary battery 51 cases 52 Electrode assembly 53 Lid plate

Claims

1. A current collector having a coating, the coating including at least a surface modification layer, the coating being formed on at least one side of the current collector, and the thickness of the surface modification layer being 100 nm to 10 μm.

2. 2. The current collector according to claim 1, wherein the thickness of the surface modification layer is 100 nm to 500 nm.

3. The density of the surface modification layer is 1.7 to 5.5 g / cm 3 and optionally 2.5 to 5.2 g / cm 3 3. The current collector according to claim 1, wherein

4. 4. The current collector according to claim 1, wherein the surface modification layer contains one or more of zinc oxide, aluminum oxide, titanium oxide, tin oxide, zirconium oxide, silicon oxide, and antimony oxide.

5. 5. The current collector according to claim 1, wherein a contact angle of a 1 mol / L solution of sodium hexafluorophosphate in ethylene glycol dimethyl ether at 25°C on the current collector having the coating is less than 50°.

6. 6. The current collector according to claim 1, wherein the surface modification layer is produced by magnetron sputtering.

7. 7. The current collector according to claim 6, wherein the high frequency power of the magnetron sputtering is 40 to 120 W, and the sputtering time is 30 seconds to 60 minutes.

8. 8. The current collector according to claim 1, wherein the surface modification layer is in direct contact with the surface of the current collector.

9. The current collector according to any one of claims 1 to 7, wherein the coating further comprises an induction deposition layer, and the induction deposition layer and the surface modification layer are provided in this order from a position closer to the current collector to a position farther from the current collector.

10. The current collector of claim 9 , wherein the induction deposition layer comprises a carbon material.

11. The current collector according to any one of claims 1 to 10, characterized in that the current collector includes at least one of a metal foil, a metal foam current collector, and a metal mesh current collector.

12. A secondary battery including a negative electrode plate, the negative electrode plate including the current collector according to any one of claims 1 to 11.

13. 13. The secondary battery according to claim 12, wherein the secondary battery is a sodium secondary battery.

14. 14. The secondary battery according to claim 12, wherein the secondary battery is a negative electrode-free sodium secondary battery.

15. The secondary battery includes a positive electrode plate, and the ratio of the thickness of the surface modification layer to the amount of positive electrode active material carried per unit area of ​​the positive electrode plate is 50 to 500 nm cm 2 15. The secondary battery according to claim 12, wherein the capacity is 1 / mAh.

16. The secondary battery according to any one of claims 12 to 15, characterized in that the secondary battery includes an electrolyte solution, the electrolyte solution includes a sodium salt, and the sodium salt includes one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

17. The secondary battery according to any one of claims 12 to 16, characterized in that after the secondary battery is subjected to 50 charge-discharge cycles, the total element mass content of Zn, Al, Ti, Sn, Zr, Si, and Sb in the electrolyte solution is less than 0.0001%, based on the total mass of the electrolyte solution.

18. An electrical device comprising a secondary battery selected from the secondary batteries according to any one of claims 12 to 17.

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