A negative electrode sheet and a lithium-ion secondary battery containing the same and capable of being discharged to zero volts

Abstract

The present invention provides a negative electrode plate and a lithium ion secondary battery containing the negative electrode plate that can be discharged to zero volts. The negative electrode plate includes a functional layer arranged on at least one side of a current collector, and the material of the functional layer includes an electrochemically active material. The negative electrode plate satisfies: the charge and discharge curve of a half-cell containing the negative electrode plate has at least one voltage platform, and the potential interval of the voltage platform satisfies 0.5V to 3.3V; or, the obtained voltage capacity differential dQ / dV curve has a redox characteristic peak in the range of 0.5V to 3.3V; or, the cyclic voltammetry curve of the half-cell test has a redox characteristic peak in the range of 0.5V to 3.3V. The negative electrode plate and the lithium ion secondary battery provided by the present invention have excellent over-discharge performance, and can meet the application requirements of lithium ion secondary batteries over-discharging to zero volts and long-term storage and circulation at zero volts.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to a negative electrode plate and a lithium-ion secondary battery containing the negative electrode plate and capable of being discharged to zero volts. Background Art

[0002] Implantable medical devices are medical devices that can be implanted in the human body and interact with human tissues to achieve treatment, auxiliary treatment or repair of human functions, so their safety and reliability are of vital importance. As one of the key components of active implantable medical devices, the performance of medical implantable batteries directly affects the life and stability of medical devices, including a series of performance indicators such as battery calendar life, storage life, self-discharge performance and over-discharge performance.

[0003] Medical implantable batteries are extremely reliable and safe due to the special properties of the entire product. Since implantable medical devices are usually designed to remain in the patient's body for a long time, the battery must be able to continue to work for 10 to 25 years without replacement. Such a design can reduce the need for secondary surgery for patients to replace batteries, thereby reducing patient risks and medical costs. Given that patients should not undergo frequent surgery after implantation, wireless charging technology can conveniently charge the battery without direct contact with the implanted device.

[0004] Since implantable medical devices usually need to work stably for a long time, the over-discharge and self-discharge of lithium-ion secondary batteries need to be strictly controlled. On the one hand, over-discharge may cause the performance of lithium-ion secondary batteries to deteriorate, or even cause dangerous situations, such as internal short circuits, which may affect the safety of the equipment. On the other hand, self-discharge may cause the lithium-ion secondary battery to run out of power prematurely, requiring more frequent replacement or charging, increasing the inconvenience of patients and medical costs.

[0005] Lithium-ion secondary batteries may have the following problems due to overdischarge: ① When lithium-ion secondary batteries are overdischarged, transition metals (such as copper, iron or nickel) in the negative electrode current collector may be oxidized and dissolved into the electrolyte. This phenomenon will cause an imbalance in the chemical substances inside the battery and affect the electrochemical reaction of the battery; ② The dissolved transition metal ions can migrate to the surface of the negative electrode active material and precipitate. The deposited metal will occupy the position originally used to embed lithium ions, reducing the reversible capacity of the battery, thereby deteriorating the battery's cycle performance; ③ When lithium-ion secondary batteries are overdischarged, transition metal ions may also precipitate to form metal dendrites, which may pierce the battery's diaphragm, causing a short circuit between the positive and negative electrodes, and even causing the battery to catch fire or explode.

[0006] In order to solve these problems, the prior art discloses the following technical means: Chinese patent CN111864277A proposes to use Ti foil to replace Cu foil for use as a negative electrode current collector, but the cost of Ti foil is much higher than that of Cu foil, and the processing performance is much worse than that of Cu foil; Chinese patent CN109860720A also discloses that a passivation layer is formed on the surface of Cu foil during the first charging process by adding an electrolyte additive to inhibit the oxidation and precipitation of copper, but since the content of the electrolyte additive is very low, it is generally consumed immediately after the SEI film is formed on the surface of the electrode, and it is difficult to further produce an effective passivation effect on the current collector at the bottom. In addition, relevant literature proposes the use of Li6CoO4 positive electrode additives to regulate the crossover potential of the positive and negative electrodes of the LiCoO2 system full battery to no more than 2.0V relative to the lithium potential when it is discharged to 0V; however, Li6CoO4 has poor air stability when used as a lithium supplement and is difficult to process. In addition, during the first electrochemical process, Li6CoO4 decomposes to form oxides, which cannot guarantee stable overdischarge performance during subsequent cycles (Wang H, Liu Y, Jiang M, et al. The Potential Regulation of Working Anode for Long-Term Zero-Volt Storage at 37℃ in Li-Ion Batteries [J]. Advanced Materials, 2400656).

[0007] Therefore, in the art, there is an urgent need to develop a lithium ion secondary battery with good overdischarge performance to solve the above problems. Summary of the invention

[0008] In view of the shortcomings of the prior art, the object of the present invention is to provide a negative electrode plate and a lithium ion secondary battery comprising the negative electrode plate and capable of being discharged to zero volts. The negative electrode plate provided by the present invention and the lithium ion secondary battery assembled therefrom have excellent overdischarge performance and can meet the application requirements of lithium ion secondary batteries being overdischarged to zero volts and being stored and cycled for a long time at zero volts.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a negative electrode plate, the negative electrode plate comprising a current collector and a functional layer disposed on at least one side of the current collector, the material of the functional layer comprising an electrochemically active material, and the negative electrode plate satisfies:

[0011] The charge-discharge curve of the half-cell containing the negative electrode sheet has at least one voltage platform, and the potential of the voltage platform is V platform , the V platformThe potential interval satisfies 0.5V≤V platform ≤3.3V;

[0012] or,

[0013] The obtained voltage-capacity differential dQ / dV curve has a redox characteristic peak in the range of 0.5V to 3.3V;

[0014] or,

[0015] The cyclic voltammetry curve of the half-cell test has a redox characteristic peak in the range of 0.5V to 3.3V.

[0016] Preferably, the electrochemically active material comprises a first electrochemically active material as shown in chemical formula (1) and / or a second electrochemically active material as shown in chemical formula (2):

[0017] Ti a M b O c A d Chemical formula (1)

[0018] Li 1+e Ti f M b M' x P y A' z Chemical formula (2)

[0019] In the chemical formula (1), a is any value from 0 to 1, b is any value from 0 to 5 / 3, c is any value from 0 to 2, d is any value from 0 to 3, M is selected from any one of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta or W, or a combination of at least two of them, and A is selected from any one of N, P, As, S, Se, Te, F, Cl, Br or I, or a combination of at least two of them.

[0020] In the chemical formula (2), b is any value from 0 to 5 / 3, e is any value from 0 to 1, f is any value from 0 to 5 / 3, x is any value from 0 to 1, y is any value from 0 to 1, z is any value from 0 to 4, M is selected from any one or a combination of at least two of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta or W, M' is selected from any one or a combination of at least two of B, Na, Mg, Al, K, Ca, Sr or Sc, and A' is selected from any one or a combination of at least two of N, O, As, S, Se, Te, F, Cl, Br or I.

[0021] Preferably, based on the total mass of the material of the functional layer being 100%, the mass percentage of the electrochemically active material is 50% to 96%.

[0022] Preferably, in the chemical formula (1), 0<(a+b) / (c+d)≤1, and A is selected from any one or a combination of at least two of S, Se or Te;

[0023] or,

[0024] In the chemical formula (2), 0<(f+b+x) / (1+e)≤2, and A' is selected from any one of O, S, Se and Te, or a combination of at least two thereof.

[0025] Preferably, the electrochemically active material comprises a first electrochemically active material and a second electrochemically active material.

[0026] Preferably, the mass ratio of the first electrochemically active material to the second electrochemically active material is (25-75):(25-75).

[0027] Preferably, the material of the functional layer further includes an adhesive and a conductive agent.

[0028] Preferably, the adhesive includes any one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, styrene-butadiene rubber or sodium carboxymethyl cellulose, or a combination of at least two thereof.

[0029] Preferably, the conductive agent includes any one of conductive carbon black, acetylene black, Ketjen black, conductive graphite flakes, carbon nanotubes, carbon nanofibers or graphene, or a combination of at least two of them.

[0030] Preferably, the thickness of the functional layer is 0.5-60 μm.

[0031] Preferably, the negative electrode plate further includes a negative electrode active material layer disposed on the surface of the functional layer.

[0032] In a second aspect, the present invention provides a lithium ion secondary battery that can be discharged to zero volts, the lithium ion secondary battery that can be discharged to zero volts comprises a positive electrode, a negative electrode, an electrolyte and a separator, the negative electrode comprises the negative electrode plate according to the first aspect, and the voltage capacity differential dQ / dV curve obtained by the lithium ion secondary battery that can be discharged to zero volts has a redox characteristic peak in the range of 0.5V to 3.3V;

[0033] or,

[0034] The cyclic voltammetry curve of the lithium ion secondary battery that can be discharged to zero volt has a redox characteristic peak in the range of 0.5V to 3.3V.

[0035] Preferably, after the charge and discharge cycle of the lithium-ion secondary battery that can be discharged to zero volt, the remaining capacity is 80% of the rated capacity.

[0036] Preferably, the discharge cut-off voltage of the lithium-ion secondary battery that can be discharged to zero volt is zero volt.

[0037] Preferably, the cyclic charge and discharge current of the lithium-ion secondary battery that can be discharged to zero volts is 0.1 to 1 times the standard capacity.

[0038] Preferably, the current collector of the negative electrode comprises a copper current collector.

[0039] Preferably, the current collector of the positive electrode comprises an aluminum current collector.

[0040] Preferably, the electrolyte comprises an electrolytic solution.

[0041] Preferably, the electrolyte comprises a lithium salt additive.

[0042] Preferably, the structure of the lithium salt additive contains at least one of fluorine, boron or phosphorus.

[0043] Preferably, the lithium salt additive includes any one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate or lithium bis(oxalatodifluorophosphate) or a combination of at least two thereof.

[0044] Preferably, based on the total mass of the electrolyte being 100%, the mass percentage of the lithium salt additive is 0.1-1 wt.%.

[0045] Preferably, the separator includes at least one of a polyolefin separator, a ceramic coating separator, a polymer coating separator or a solid electrolyte coating separator.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention provides a negative electrode plate. When the lithium secondary battery assembled by the negative electrode plate is over-discharged to 0V, the positive and negative electrode potentials can be controlled not to be higher than the oxidation potential of the transition metal in the current collector, thereby effectively preventing the transition metal in the current collector from oxidizing and dissolving, inhibiting the metal ions from being freed into the electrolyte and precipitating from the negative electrode side with low potential in the next charge and discharge process, and avoiding the phenomenon of hindering the rapid transmission of lithium ions and the formation of transition metal dendrites piercing the diaphragm, thereby finally improving the cycle capacity retention rate, calendar life and safety performance of the lithium ion secondary battery, so that the lithium ion secondary battery has excellent zero-volt cycle and zero-volt storage recovery start-up capabilities, and solves the technical problems in the prior art that when the battery is over-discharged, the transition metal in the negative electrode current collector (including but not limited to copper, iron, nickel, etc.) is oxidized into ions and precipitated on the negative electrode side, causing the cycle life and calendar life of the battery to deteriorate, and the transition metal dendrites pierce the diaphragm, resulting in a short circuit between the positive and negative electrodes, and causing extreme thermal runaway such as battery fire or explosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the charge and discharge curve characteristics of a lithium half-cell that the negative electrode current collector functional layer needs to have in the first aspect of the embodiment of the present invention;

[0049] Figure 2 The 0.1C / 0.1C charge-discharge curve characteristics of several negative electrode current collector functional layers for lithium half-cells are listed in the first aspect of the embodiment of the present invention but should not be interpreted as exhaustive;

[0050] Figure 3 The voltage capacity differential dQ / dV curves obtained by the 0.1C / 0.1C charge-discharge curve of the lithium half-cell of several negative electrode current collector functional layers listed in the first aspect of the embodiment of the present invention but should not be interpreted as exhaustive;

[0051] Figure 4 Li4Ti5O is listed in the first aspect of the embodiment of the present invention but should not be interpreted as an exhaustive list. 12 Cyclic voltammetry curve of functional layer;

[0052] Figure 5 The cyclic voltammetry curve of the copper current collector without a functional layer coated with lithium according to the first aspect of the embodiment of the present invention;

[0053] Figure 6 The charge and discharge curve of the lithium-ion secondary battery that can be discharged to zero volts and is prepared by coating the negative electrode current collector functional layer according to the second aspect of the embodiment of the present invention;

[0054] Figure 7 The third embodiment of the present invention is a full battery, positive electrode and negative electrode potential curve measured by three electrodes during the charge and discharge process of a lithium-ion secondary battery that can be discharged to zero volts and is prepared by coating a negative electrode current collector functional layer;

[0055] Figure 8 The third aspect of the present invention is to convert the full battery, positive electrode and negative electrode potential curves measured by three electrodes during the charge and discharge process of the lithium ion secondary battery that can be discharged to zero volts and is prepared by coating the negative electrode current collector functional layer into a voltage capacity differential dQ / dV curve;

[0056] Fig. 9 The zero volt discharge cycle capacity retention rate curve of a full battery prepared by coating with several negative electrode current collector functional layers is listed in the second aspect of the embodiment of the present invention but should not be interpreted as an exhaustive list;

[0057] Fig.10 It is a schematic diagram of the structure of a lithium-ion secondary battery in the second aspect of an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0059] For simplicity, the present invention only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the endpoints of the range is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0060] In the description of the present invention, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and the “multiple” in “one or more” means more than two, and the “multiple” in “one or more” means more than two.

[0061] The above summary of the invention of the present invention is not intended to describe each disclosed embodiment or each implementation in the present invention. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0062] Negative electrode

[0063] A first aspect of an embodiment of the present invention provides a negative electrode plate, which includes a current collector and a functional layer and a negative electrode active material layer stacked in sequence on at least one side of the current collector, wherein the material of the functional layer includes an electrochemically active material, a conductive agent and an adhesive.

[0064] The method for preparing the functional layer exemplarily includes preparing a slurry of an electrochemically active material, a conductive agent and an adhesive according to a certain formula ratio, uniformly coating the slurry on both sides of a current collector including but not limited to copper material, and obtaining the functional layer after drying.

[0065] like Figure 1-Figure 3 As shown, the electrochemically active material has electrochemical activity to lithium. The negative electrode plate and lithium metal are assembled into a half-cell. The charge and discharge curve of the half-cell has at least one voltage platform. The potential of the voltage platform is V platform , V platform The potential interval satisfies 0.5V≤V platform ≤3.3V;

[0066] or,

[0067] The obtained voltage-capacity differential dQ / dV curve has a redox characteristic peak in the range of 0.5V to 3.3V;

[0068] or,

[0069] The cyclic voltammetry curve of the half-cell test has a redox characteristic peak in the range of 0.5V to 3.3V.

[0070] In the present invention, the voltage platform has a well-known meaning in the field of electrochemistry. However, in order to avoid the interference of the non-material intrinsic electrochemical potential platform caused by polarization, the voltage platform formed by the current charge and discharge of 0.1 to 1C is limited as the voltage platform V referred to in the present invention. platform The voltage platform can be measured by a charge and discharge cabinet. As an example, the negative electrode sheet is cut into 12 mm pieces with a cutting knife, the mass of the negative electrode sheet is weighed, the moisture is dried, and a lithium 2032 button battery is made in an argon atmosphere in a glove box. The 2032 button battery is charged and discharged with a small current, and at least one voltage platform can be obtained according to the charge and discharge curve.

[0071] In some embodiments, the electrochemically active material includes a first electrochemically active material as shown in chemical formula (1) and / or a second electrochemically active material as shown in chemical formula (2):

[0072] Ti a M b O c A d Chemical formula (1)

[0073] In the chemical formula (1), a is any value from 0 to 1, b is any value from 0 to 5 / 3, c is any value from 0 to 2, and d is any value from 0 to 3. a, b, c, and d may be any values ​​within the assigned range, and may include decimals, for example, a may be 0.5, and d may be 1.5; M is selected from any one of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta, or W, or a combination of at least two thereof; and A is selected from any one of N, P, As, S, Se, Te, F, Cl, Br, or I, or a combination of at least two thereof.

[0074] Li 1+e Ti f M b M' x P y A' z Chemical formula (2)

[0075] In the chemical formula (2), b is any value from 0 to 5 / 3, e is any value from 0 to 1, f is any value from 0 to 5 / 3, x is any value from 0 to 1, y is any value from 0 to 1, and z is any value from 0 to 4. b, e, f, x, y, and z can be any values ​​within the assigned range, and can exemplarily include decimals, for example, b can be 0.5, and f can be 1.0; M is selected from any one or a combination of at least two of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta, or W, M' is selected from any one or a combination of at least two of B, Na, Mg, Al, K, Ca, Sr, or Sc, and A' is selected from any one or a combination of at least two of N, O, As, S, Se, Te, F, Cl, Br, or I.

[0076] In the present invention, the stoichiometric values ​​in the above chemical formula can be arbitrarily matched within the numerical range and do not need to satisfy the maximum or minimum values ​​at the same time. As an example, the material in chemical formula (1) can be Ti 0.5 O, can also be Ti 0.5 O 0.5 .

[0077] like Figure 4-5 As shown, both the first electrochemically active material and the second electrochemically active material have electrochemical activity to lithium, and there is a stable charge and discharge voltage platform when the electrochemical reaction occurs. The emergence of this voltage platform regulates that when the full battery is over-discharged to zero volts, the negative electrode potential does not rise to above the oxidation potential of the transition metal current collector including but not limited to copper, thereby reducing the oxidation precipitation of the current collector and the decomposition of the SEI film on the negative electrode side.

[0078] In some embodiments, based on the total mass of the material of the functional layer as 100%, the mass percentage of the electrochemically active material is 50% to 96%, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, etc.

[0079] In some more preferred embodiments, in chemical formula (1), 0<(a+b) / (c+d)≤1, and A is selected from any one of S, Se or Te or a combination of at least two thereof, for example, it can be TiO2, MnO2, VO2, TiS2, FeS2, CuS, MoS2, MoS3, Mo6S8 or V5S8, etc.

[0080] In some preferred embodiments, in the chemical formula (2), 0<(f+b+x) / (1+e)≤2, and A' is selected from any one or a combination of at least two of O, S, Se or Te, for example, Li4Ti5O 12 、Li4Mn5O 12 or LiFePO4.

[0081] In some preferred embodiments, the negative electrode sheet comprising the first electrochemically active material and / or the second electrochemically active material is assembled with lithium metal into a half-cell, and the potential of the voltage platform of the corresponding charge-discharge curve is V platform , V platform The potential interval satisfies 0.5V≤V platform ≤2.5V.

[0082] In some more preferred embodiments, the negative electrode sheet comprising the first electrochemically active material and / or the second electrochemically active material is assembled with lithium metal into a half-cell, and the obtained voltage capacity differential dQ / dV curve has a redox characteristic peak in the potential range of 0.5V to 2.5V.

[0083] In some more preferred embodiments, the negative electrode sheet comprising the first electrochemically active material and / or the second electrochemically active material is assembled with lithium metal into a half-cell, and the tested cyclic voltammetry curve has a redox characteristic peak in the range of 0.5V to 2.5V.

[0084] In some more preferred embodiments, the electrochemically active material includes a first electrochemically active material and a second electrochemically active material.

[0085] In some more preferred embodiments, the mass ratio of the first electrochemically active material to the second electrochemically active material is (25-75):(25-75), for example, it can be 25:75, 28:72, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, etc.

[0086] In the present invention, by regulating the mass ratio of the first electrochemically active material and the second electrochemically active material, the number of electrochemical platform segments and the voltage value of the platform of the functional layer can be changed. For example, by changing the first electrochemically active material having a lower platform voltage, the platform potential of the overall functional layer can be reduced, thereby regulating the positive and negative electrode crossover potential to a lower level and avoiding oxidation of the negative electrode current collector; or, for example, by improving the first electrochemically active material having multiple electrochemical platforms, the functional layer can have more platforms, thereby regulating the negative electrode side potential to present a multi-stage platform feature, inhibiting the rapid rise of the positive and negative electrode crossover potential, and achieving the effect of avoiding oxidation of the negative electrode current collector.

[0087] In some embodiments, the adhesive includes any one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, styrene-butadiene rubber or sodium carboxymethyl cellulose, or a combination of at least two thereof.

[0088] In some more preferred embodiments, the adhesive is polyvinylidene fluoride.

[0089] In some embodiments, the conductive agent includes any one of conductive carbon black, acetylene black, Ketjen black, conductive graphite flakes, carbon nanotubes, carbon nanofibers, or graphene, or a combination of at least two thereof.

[0090] In some more preferred embodiments, the conductive agent includes conductive graphite flakes and / or acetylene black.

[0091] In some embodiments, the thickness of the functional layer is 0.5 to 60 μm, for example, 0.5 μm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, etc.

[0092] In some more preferred embodiments, the thickness of the functional layer is 0.5-10 μm.

[0093] Lithium-ion secondary battery that can be discharged to zero volts

[0094] A second aspect of an embodiment of the present invention provides a lithium ion secondary battery that can be discharged to zero volts. The lithium ion secondary battery that can be discharged to zero volts includes a positive electrode, a negative electrode, an electrolyte and a separator. The negative electrode includes the above-mentioned negative electrode plate, such as Figure 6-Figure 8 As shown, the voltage capacity differential dQ / dV curve obtained by the lithium-ion secondary battery that can be discharged to zero volts has a redox characteristic peak in the range of 0.5V to 3.3V;

[0095] or,

[0096] The cyclic voltammetry curve of a lithium-ion secondary battery that can be discharged to zero volts has a redox characteristic peak in the range of 0.5V to 3.3V.

[0097] In some embodiments, after the lithium-ion secondary battery that can be discharged to zero volts undergoes charge and discharge cycles, the remaining capacity is 80% of the rated capacity.

[0098] In some embodiments, the discharge cut-off voltage of the lithium-ion secondary battery that can be discharged to zero volt is zero volt.

[0099] In some embodiments, the cyclic charge and discharge current of the lithium-ion secondary battery that can be discharged to zero volts is 0.1 to 1 times the standard capacity.

[0100] In some embodiments, the negative electrode current collector may be a metal foil or a porous metal plate or a non-metal fiber, for example, a copper, nickel, titanium, silver, aluminum, carbon fiber, stainless steel or related metal alloy foil or a porous plate, such as copper foil.

[0101] In some embodiments, the active material of the negative electrode includes but is not limited to graphite, silicon-carbon material, silicon-oxygen material, hard carbon, soft carbon, or mesophase carbon microspheres.

[0102] In some more preferred embodiments, the active material of the negative electrode includes but is not limited to at least one of graphite, silicon-carbon material or silicon-oxygen material.

[0103] In some embodiments, the negative electrode can be prepared by transfer coating, extrusion coating or gravure coating. For example, the negative electrode active material, binder, conductive agent and solvent are first mixed in a predetermined ratio to obtain a mixed material, and the organic solvent can be deionized water. The mixed material is stirred to a uniform system to obtain a negative electrode slurry; then the negative electrode slurry is coated on the negative electrode current collector, and after drying and rolling processes, the negative electrode is obtained.

[0104] In some embodiments, the current collector of the positive electrode may be a metal foil or a porous metal plate, for example, a copper, nickel, titanium, silver, aluminum, stainless steel, or alloy foil or a porous plate of related metals, such as aluminum foil.

[0105] In some embodiments, the positive electrode active material of the positive electrode includes but is not limited to at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium ferrous phosphate, lithium manganese oxide, lithium iron manganese phosphate, or a lithium-rich manganese-based layered oxide material.

[0106] In some more preferred embodiments, the positive electrode active material of the positive electrode includes but is not limited to at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide 111 (NCM111), lithium nickel cobalt manganese oxide 523 (NCM523), lithium nickel cobalt manganese oxide 622 (NCM622), lithium nickel cobalt manganese oxide 811 (NCM811), lithium manganese oxide (LiMn2O4) or lithium ferrous phosphate (LiFePO4).

[0107] In some embodiments, the positive electrode can be prepared by transfer coating, extrusion coating or gravure coating. For example, the positive electrode active material, binder, conductive agent and organic solvent are first mixed in a predetermined ratio to obtain a mixed material, the organic solvent can be N-methylpyrrolidone (NMP), the mixed material is stirred to a uniform system to obtain a positive electrode slurry; then the positive electrode slurry is coated on the positive electrode current collector, and after drying and rolling processes, the positive electrode is obtained.

[0108] In some embodiments, the electrolyte includes an electrolytic solution.

[0109] In some embodiments, the electrolyte includes a lithium salt, a solvent, and an additive, which plays a role in transmitting ions between the positive and negative electrodes.

[0110] In some embodiments, the solvent is a non-aqueous organic solvent, for example, a combination of any one or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), fluoropropylene carbonate (FPC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB), preferably a combination of at least two.

[0111] In some more preferred embodiments, the solvent includes a combination of at least two of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and dimethyl carbonate (DMC).

[0112] In some embodiments, the lithium salt uses a lithium-containing compound with a higher degree of ionization, for example, it may include any one or more combinations of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluorosulfonyl)imide (LiTFSI).

[0113] In some more preferred embodiments, the lithium salt includes a combination of lithium hexafluorophosphate (LiPF6) and a small amount of at least one other lithium salt.

[0114] In some embodiments, the electrolyte includes a lithium salt additive.

[0115] In the present invention, the role of the lithium salt additive is to form a stable solid electrolyte layer at the interface between the positive and negative electrodes to prevent the electrodes from continuously reacting with the electrolyte under high or low pressure.

[0116] In some embodiments, the structure of the lithium salt additive contains at least one of fluorine, boron or phosphorus.

[0117] In some embodiments, the lithium salt additive includes any one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, or lithium bis(oxalatodifluorophosphate), or a combination of at least two thereof.

[0118] In some embodiments, based on the total mass of the electrolyte being 100%, the mass percentage of the lithium salt additive is 0.1-1 wt.%.

[0119] In some embodiments, the electrolyte further includes other additives.

[0120] In some embodiments, other additives include solid organic powders and liquid organics.

[0121] In some embodiments, the solid organic powder includes any one or a combination of at least two of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), methylene methanedisulfonate (MMDS), 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST) and diethylene sulfate (DTD).

[0122] In some more preferred embodiments, the solid organic powder includes a combination of at least two of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methylene methanedisulfonate (MMDS), 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST) and diethylene sulfate (DTD).

[0123] In some embodiments, based on the total mass of the electrolyte as 100%, the mass percentage of the solid organic powder is 0.1-4%, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, etc.

[0124] In some embodiments, the liquid organic material includes any one or a combination of at least two of bis(2,2,2-trifluoroethyl) carbonate (TFEC), triethyl borate (TEB), trimethoxyboroxine (TMEB) and diethyl bisfluorocarbonate (DFDEC).

[0125] In some embodiments, the separator includes at least one of a polyolefin separator, a ceramic coating separator, a polymer coating separator, or a solid electrolyte coating separator, but the present invention is not limited thereto.

[0126] like Fig. 9As shown, the lithium-ion secondary battery assembled by the negative electrode plate provided by the present invention can effectively prevent the current collector from dissolving when the battery is over-discharged, thereby improving the cycle capacity retention rate of the lithium-ion secondary battery, so that the lithium-ion secondary battery has the ability of zero-volt cycling and zero-volt storage recovery startup, and the specific performance can be demonstrated through embodiments.

[0127] Example

[0128] The following examples describe the disclosure of the present invention in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0129] Example 1

[0130] This embodiment provides a negative electrode sheet and a lithium-ion secondary battery assembled therefrom, such as Fig.10 As shown, the preparation method comprises the following steps:

[0131] Positive electrode preparation

[0132] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black and polyvinylidene fluoride binder are dispersed in N-methylpyrrolidone solvent and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting and cutting, the positive electrode sheet is obtained. The weight ratio of positive electrode active material, conductive carbon black and polyvinylidene fluoride binder is 96:2:2.

[0133] Functional layer preparation

[0134] A certain proportion of the first electrochemically active material, the second electrochemically active material, conductive carbon black and polyvinylidene fluoride binder are dispersed in an N-methylpyrrolidone solvent and mixed evenly to obtain a functional layer slurry; the functional layer slurry is evenly coated on the negative electrode current collector copper foil.

[0135] Negative electrode preparation

[0136] The negative electrode active material graphite, conductive carbon black, sodium carboxymethyl cellulose thickener and styrene butadiene latex binder are dispersed in deionized water and mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the copper foil current collector with a functional layer, and after drying, cold pressing, slitting and cutting, a negative electrode sheet is obtained. The weight ratio of the negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose thickener and styrene butadiene latex binder is 95:2:1:2.

[0137] Preparation of basic electrolyte

[0138] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and diethyl carbonate (DMC) were mixed uniformly at a mass ratio of 30:50:10:10 to obtain a non-aqueous organic solvent. LiPF6 with a concentration of 1.2 mol / L was dissolved in the non-aqueous organic solvent and mixed uniformly, and then 0.5% VC, 1% PS and 1% LiDFOB were added to obtain an electrolyte solution based on the total mass of the electrolyte solution as 100%.

[0139] Lithium-ion secondary battery preparation

[0140] The positive electrode sheet, the isolation membrane and the negative electrode sheet are stacked in sequence. The isolation membrane is made of a polyethylene composite film coated with aluminum oxide. They are then wound into a battery cell and loaded into a soft-pack shell. After processes such as top and side sealing and electrolyte injection, a soft-pack battery is made.

[0141] Examples 2 to 35 and Comparative Example 1

[0142] The difference between Examples 2 to 35 and Example 1 is that the relevant parameters such as the positive electrode material, negative electrode material, electrochemically active material, ratio and thickness of the lithium-ion secondary battery are adjusted; further, the difference between Examples 31 to 35 and Comparative Example 1 is that on the premise of coating the functional layer, some additives are added to the basic electrolyte, and the details are shown in Table 1.

[0143] Lithium-ion secondary battery testing

[0144] 1) Lithium-ion battery composition and capacity

[0145] Under 25℃ environment, place it for 30min, charge it with 0.1C constant current to the specified potential, place it for 10min, discharge it with 0.1C constant current to the specified potential (ternary system 2.8~4.25V, lithium iron phosphate system 2.0~3.65V, lithium manganate system 3.0~4.3V, lithium cobalt oxide system 3.0~4.45V).

[0146] 2) Over discharge cycle test

[0147] Under 25℃ environment, place it for 30min, charge it at 0.3C constant current to the specified voltage, place it for 10min, and discharge it at 0.3C constant current to 0V. This is one charge and discharge cycle, and the discharge capacity is recorded as the discharge capacity of the first cycle of the lithium-ion secondary battery. Perform cyclic charge and discharge tests on the lithium-ion secondary battery according to the above method, and record the discharge capacity of each cycle.

[0148] Under 25°C environment, the capacity retention rate of the nth cycle of 0.3C / 0.3C zero volt overdischarge of lithium-ion secondary battery (%) = (nth cycle discharge capacity / 1st cycle discharge capacity) × 100%. Record the number of lithium-ion cycle life when the cycle capacity reaches 80%.

[0149] The test results of Examples 1 to 35 and Comparative Example 1 are shown in Table 2.

[0150] Table 1

[0151]

[0152]

[0153]

[0154]

[0155] Table 2

[0156]

[0157]

[0158]

[0159] It can be seen from Table 2 that compared with Comparative Example 1 which only uses a copper current collector, the present invention can effectively suppress the positive and negative electrode crossover potential from exceeding the copper current collector oxidation potential when over-discharging to zero volts by constructing a functional coating with one or more platform potentials on the negative electrode side, thereby significantly improving the zero-volt over-discharge cycle and storage performance of the lithium-ion battery, so that it can be applied to an implantable medical device system; at the same time, the present invention can also improve the zero-volt over-discharge cycle and storage performance of the lithium-ion battery by preferably improving the composition of the electrolyte additive, indicating that the synergistic effect between the functional layer and the electrolyte additive can further improve the zero-volt over-discharge cycle and storage performance of the lithium-ion battery, and enable it to have a long calendar life.

[0160] By comparing Example 2 and Example 16-Example 18, it can be seen that as the content of the first electrochemically active material continues to increase, the voltage value of the electrochemical platform of the negative electrode functional layer gradually decreases, thereby further regulating the positive and negative electrode crossover potential to a lower level to avoid oxidation of the negative electrode current collector. Furthermore, by comparing Example 17 and Example 19-Example 21, it can be seen that the present invention can further reduce the platform potential of the overall functional layer by replacing the second electrochemically active material with a different type of the first electrochemically active material.

[0161] By comparing Example 2 and Example 22 to Example 30, it can be seen that the present invention further improves the zero-volt over-discharge cycle and storage performance of the lithium-ion battery by preferentially selecting different types of negative electrode active materials and different types of positive electrode active materials.

[0162] Comparative Example 2 shows that although replacing the material of the current collector with titanium foil improves the overdischarge performance of the lithium-ion battery to a certain extent, the cost of titanium foil is relatively high, which is not conducive to large-scale production.

[0163] Comparative Example 3 shows that even if an electrolyte additive capable of passivating the copper current collector is used, all the technical effects of the technical solution provided by the present invention cannot be achieved.

[0164] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negative electrode plate, comprising a current collector and a functional layer arranged on at least one side of the current collector, characterized in that: The material of the functional layer includes an electrochemically active material, and the negative electrode plate meets the following requirements: The charge-discharge curve of the half-cell containing the negative electrode sheet has at least one voltage platform, and the potential of the voltage platform is V platform , V platform The potential interval satisfies 0.5V≤ V platform ≤3.3V; or, The obtained voltage-capacity differential dQ / dV curve has a redox characteristic peak in the range of 0.5V to 3.3V; or, The cyclic voltammetry curve of the half-cell test has a redox characteristic peak in the range of 0.5V to 3.3V; The electrochemically active material comprises a first electrochemically active material as shown in chemical formula (1) and / or a second electrochemically active material as shown in chemical formula (2): Ti a M b O c A d Chemical formula (1) Li 1+e Ti f M b M’ x P y A’ z Chemical formula (2) In the chemical formula (1), a is any value from 0 to 1, b is any value from 0 to 5 / 3, c is any value from 0 to 2. d is any value from 0 to 3, M is selected from any one or a combination of at least two of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta or W, and A is selected from any one or a combination of at least two of N, P, As, S, Se, Te, F, Cl, Br or I; In the chemical formula (2), b is any value from 0 to 5 / 3, e is any value from 0 to 1, f is any value from 0 to 5 / 3, x is any value from 0 to 1, y is any value from 0 to 1, z is any value from 0 to 4, M is selected from any one or a combination of at least two of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Cd, Ta or W, M' is selected from any one or a combination of at least two of B, Na, Mg, Al, K, Ca, Sr or Sc, A' is selected from any one or a combination of at least two of N, O, As, S, Se, Te, F, Cl, Br or I; Taking the total mass of the material of the functional layer as 100%, the mass percentage of the electrochemically active material is 50% to 96%.

2. The negative electrode sheet according to claim 1, characterized in that: In the chemical formula (1), 0<(a+b) / (c+d)≤1, and A is selected from any one of S, Se or Te or a combination of at least two thereof; or, In the chemical formula (2), 0<(f+b+x) / (1+e)≤2, and A' is selected from any one of O, S, Se and Te, or a combination of at least two thereof.

3. The negative electrode sheet according to claim 1, characterized in that: The electrochemically active material includes a first electrochemically active material and a second electrochemically active material; The mass ratio of the first electrochemically active material to the second electrochemically active material is (25-75):(25-75).

4. The negative electrode sheet according to claim 1, characterized in that: The material of the functional layer also includes an adhesive and a conductive agent; The adhesive includes any one of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyacrylic acid, styrene-butadiene rubber or sodium carboxymethyl cellulose, or a combination of at least two thereof; The conductive agent includes any one or a combination of at least two of conductive carbon black, acetylene black, Ketjen black, conductive graphite flakes, carbon nanotubes, carbon nanofibers or graphene; The thickness of the functional layer is 0.5-60 μm; The negative electrode plate further includes a negative electrode active material layer disposed on the surface of the functional layer.

5. A lithium ion secondary battery capable of being discharged to zero volts, the lithium ion secondary battery capable of being discharged to zero volts comprising a positive electrode, a negative electrode, an electrolyte and a separator, characterized in that: The negative electrode comprises a negative electrode plate according to any one of claims 1 to 4, and the voltage capacity differential dQ / dV curve obtained by the lithium-ion secondary battery that can be discharged to zero volts has a redox characteristic peak in the range of 0.5V to 3.3V; or, The cyclic voltammetry curve of the lithium ion secondary battery that can be discharged to zero volt has a redox characteristic peak in the range of 0.5V to 3.3V.

6. The lithium-ion secondary battery capable of being discharged to zero volts according to claim 5, characterized in that: After the lithium-ion secondary battery that can be discharged to zero volts has a residual capacity of 80% of the rated capacity after charge and discharge cycles; The discharge cut-off voltage of the lithium-ion secondary battery that can be discharged to zero volt is zero volt; The cyclic charge and discharge current of the lithium ion secondary battery that can be discharged to zero volt is 0.1 to 1 times of the standard capacity.

7. The lithium-ion secondary battery capable of being discharged to zero volts according to claim 5 or 6, characterized in that: The current collector of the negative electrode comprises a copper current collector; The current collector of the positive electrode includes an aluminum current collector.

8. The lithium-ion secondary battery capable of being discharged to zero volts according to claim 5, characterized in that: The electrolyte includes an electrolyte solution; The electrolyte includes a lithium salt additive; The structure of the lithium salt additive contains at least one of fluorine, boron or phosphorus; The lithium salt additive includes any one of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate or lithium bis(oxalatodifluorophosphate) or a combination of at least two thereof; Taking the total mass of the electrolyte as 100%, the mass percentage of the lithium salt additive is 0.1-1wt.%.

9. The lithium-ion secondary battery capable of being discharged to zero volts according to claim 5, characterized in that: The separator includes at least one of a polyolefin separator, a ceramic coating separator, a polymer coating separator or a solid electrolyte coating separator.

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