CN115832184A

CN115832184A - Lithium-free negative pole piece and preparation method thereof, secondary battery, battery module, battery pack and electric device

Info

Publication number: CN115832184A
Application number: CN202210704136.5A
Authority: CN
Inventors: 张翠平; 韩昌隆; 王扶林; 范朋
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-06-21
Filing date: 2022-06-21
Publication date: 2023-03-21

Abstract

The application provides a no lithium negative pole piece, including negative pole mass flow body and negative pole active material layer. The negative active material layer is arranged on the surface of the negative current collector; the negative active material layer includes a transition metal salt. After formation, a solid electrolyte interface film rich in transition metal ions can be formed on the surface of the lithium-free negative pole piece, so that the dissolution of transition metal in electrolyte and a positive active material can be inhibited, the negative pole piece is prevented from being deteriorated, and the cycle life of the lithium-free negative pole piece for preparing a secondary battery is longer.

Description

Lithium-free negative pole piece and preparation method thereof, secondary battery, battery module, battery pack and electric device

Technical Field

The application relates to the field of secondary batteries, in particular to a lithium-free negative electrode plate, a preparation method thereof, a secondary battery, a battery module, a battery pack and an electric device.

Background

Lithium ion batteries are of great interest because of their high specific energy, long cycle life, low self-discharge, good safety, and the like. However, in the use process of the lithium ion battery, as the positive active material deteriorates, the transition metal element contained in the positive active material gradually dissolves out and migrates to the interface of the negative electrode plate, which causes deterioration of the negative electrode plate and affects the cycle life of the battery.

Disclosure of Invention

Based on the above problems, the present application provides a lithium-free negative electrode plate, a method for manufacturing the same, a secondary battery, a battery module, a battery pack, and an electric device, so as to improve the cycle life of the conventional secondary battery.

In one aspect of the present application, there is provided a lithium-free negative electrode sheet, including:

a negative current collector; and

a negative electrode active material layer disposed on a surface of the negative electrode current collector; the negative active material layer includes a transition metal salt.

According to the lithium-free negative pole piece, the negative active material layer contains the transition metal salt, and after the secondary battery is formed, a Solid Electrolyte Interface (SEI) film rich in transition metal ions can be formed on the surface of the lithium-free negative pole piece.

In some of these embodiments, the transition metal element in the transition metal salt comprises at least one of Co, ni, mn, fe, cu, zn, cr, V, and Ti.

In some embodiments, the content of the transition metal element in the anode active material layer is 10ppm to 850ppm;

optionally, in the anode active material layer, the content of the transition metal element is 20ppm to 800ppm;

optionally, in the anode active material layer, the content of the transition metal element is 20ppm to 500ppm;

optionally, in the anode active material layer, the content of the transition metal element is 20ppm to 200ppm.

The content of the transition metal element is too high or too low, which is not beneficial to improving the cycle life of the secondary battery, and the content of the transition metal element in the negative active material layer is adjusted to be within the range, so that the secondary battery has better cycle life.

In some of these embodiments, the transition metal salt comprises at least one of a nitrate, oxalate, sulfonate, acetate, and carbonate;

optionally, the transition metal salt is selected from at least one of nitrate, oxalate, sulfonate, and acetate.

In some embodiments, the distribution depth of the transition metal salt is 10nm to 100nm in a direction from the surface of the negative electrode active material layer away from the negative electrode current collector toward the negative electrode current collector;

optionally, the distribution depth of the transition metal salt is 30nm to 80nm.

The transition metal salt is mainly distributed on the surface of the negative active material layer far away from the negative current collector, and is beneficial to forming an SEI film rich in transition metal ions on the surface of the lithium-free negative pole piece.

In some of these embodiments, the negative active material in the negative active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase micro carbon spheres, a silicon-based material, and a tin-based material.

In a second aspect, the present application further provides a method for preparing a lithium-free negative electrode plate, including the following steps:

preparing a negative active material layer on at least one surface of a negative current collector, and preparing a lithium-free pole piece;

the lithium-free electrode sheet is soaked in a solution containing a transition metal salt to allow the transition metal salt to penetrate into the negative active material layer.

The preparation method enables the active material layer of the lithium-free negative pole piece to contain the transition metal salt through soaking, and the preparation method is simple and easy to realize; and after the prepared lithium-free negative pole piece is subjected to formation treatment, an SEI film rich in transition metal ions can be formed on the surface of the lithium-free negative pole piece, so that the cycle life of the secondary battery is favorably prolonged.

The cycle life of the secondary battery is not favorably improved due to too high or too low content of the transition metal element, and the cycle life of the secondary battery is better due to the fact that the content of the transition metal element in the negative electrode active material layer is adjusted to be within the range.

optionally, the depth of distribution of the transition metal salt is 30nm to 80nm.

In some of these embodiments, the solvent of the solution is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, and tetrahydrofuran;

optionally, the solvent of the solution is dimethyl carbonate.

In some of these embodiments, the mass percentage of the transition metal salt in the solution is 1% to 30%;

optionally, the mass percentage of the transition metal salt in the solution is 5% to 10%.

In some embodiments, the soaking time is 15min to 180min.

In a third aspect, the present application further provides a secondary battery, including the lithium-free negative electrode plate or the lithium-free negative electrode plate prepared according to the preparation method of the lithium-free negative electrode plate.

In some of these embodiments, the secondary battery further includes a positive electrode active material; the positive electrode active material contains a transition metal element.

In some of these embodiments, the positive active material is selected from Li [ Ni ] _x Co _y N _z M _1-x-y-z ]O ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₃ ·(1-a)LiAO ₂ And LiFePO ₄ At least one of;

wherein N is selected from one of Mn and Al; m is selected from one of Co, ni, mn, mg, cu, zn, al, sn, B, ga, cr, sr, V and Ti; x is more than or equal to 0 and less than 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is less than or equal to 1;

a is selected from one of Ni, co and Mn; a is more than 0 and less than 1.

In some of these embodiments, the transition metal element of the lithium-free negative electrode tab is the same as the transition metal element in the positive electrode active material.

In some of these embodiments, the secondary battery further comprises an electrolyte; the electrolyte comprises an additive;

optionally, the additive is selected from at least one of vinylene carbonate, vinyl sulfate, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate, fluoroethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, and 1,3 propane sultone.

In some of the embodiments, the mass percentage of the additive in the electrolyte is 0.1-5%;

optionally, in the electrolyte, the mass percentage of the additive is 0.5% to 2%.

In a fourth aspect, the present application also provides a battery module including the secondary battery described above.

In a fifth aspect, the present application further provides a battery pack including the above battery module.

In a sixth aspect, the present application further provides an electric device including at least one selected from the group consisting of the secondary battery described above, the battery module described above, and the battery pack described above.

The foregoing description is only an overview of the technical solutions of the present application, and the present application can be implemented according to the content of the description in order to make the technical means of the present application more clearly understood, and the following detailed description of the present application is given in order to make the above and other objects, features, and advantages of the present application more clearly understandable.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the alternative embodiments. The drawings are only for purposes of illustrating alternative embodiments and are not to be construed as limiting the application. Moreover, like reference numerals are used to refer to like elements throughout. In the drawings:

fig. 1 is a schematic view of a secondary battery according to an embodiment of the present application;

fig. 2 is an exploded view of a secondary battery according to an embodiment of the present application shown in fig. 1;

fig. 3 is a schematic view of a battery module according to an embodiment of the present application;

fig. 4 is a schematic view of a battery pack according to an embodiment of the present application;

fig. 5 is an exploded view of the battery pack of fig. 4 according to an embodiment of the present application;

fig. 6 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source;

description of reference numerals:

1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 cover plate; 6 electric device.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present application are shown in the drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The positive active material in the traditional lithium ion battery mostly adopts ternary materials containing transition metal elements, lithium iron phosphate, lithium manganese iron phosphate and the like. During the use of a lithium ion battery, transition metal ions of the positive electrode active material are generally eluted with the deterioration of the positive electrode active material. The inventor of the application finds that the dissolved transition metal ions are easy to deposit on the surface of the negative pole piece and damage an SEI (solid electrolyte interphase) film on the surface of the negative pole piece, so that a large amount of active lithium of the lithium ion battery is consumed, and the cycle life of the battery is influenced.

The application provides a lithium-free negative pole piece, a preparation method thereof, a secondary battery using the lithium-free negative pole piece, a battery module, a battery pack and an electric device. The secondary battery has a long cycle life, and is suitable for various electric devices using batteries, such as mobile phones, portable devices, notebook computers, battery cars, electric toys, electric tools, electric automobiles, ships, spacecrafts and the like, and the spacecrafts comprise airplanes, rockets, space shuttles, spacecrafts and the like.

The application provides a no lithium negative pole piece, including negative current collector and negative active material layer. The negative active material layer is arranged on the surface of the negative current collector; the negative active material layer includes a transition metal salt. As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two surfaces opposite to the negative electrode current collector.

It can be understood that the lithium-free negative electrode plate provided by the embodiment of the present application does not include a metal lithium layer.

Specifically, regarding the content of the transition metal element in the lithium-free negative electrode piece, the lithium-free negative electrode piece can be obtained by disassembling, an ICP test is performed on one part of the lithium-free negative electrode piece to obtain the content of the transition metal ion X1ppm, the other part of the lithium-free negative electrode piece is soaked in a solution containing the transition metal ion for 3 hours, the surface is cleaned by DMC, the ICP test is performed to obtain the content of the transition metal ion X2, if the test X1 is close to the test X1, the lithium-free negative electrode piece contains the transition metal element, and if the ratio X2/X1 is more than or equal to 5, the lithium-free negative electrode piece does not contain the transition metal element.

In addition, the lithium-free negative electrode piece can be tested by adopting a scanning electron microscope-energy spectrometer (SEM-EDS) according to the standard of GB/T17359-2012 quantitative analysis by microbeam analysis energy spectrometry, and the element distribution on the surface of the lithium-free negative electrode piece can be observed.

In some of the embodiments, the transition metal element in the transition metal salt includes at least one of Co, ni, mn, fe, cu, zn, cr, V, and Ti.

In some of the embodiments, the content of the transition metal element in the anode active material layer is 10ppm to 850ppm. The content of the transition metal element is too low, the content of an SEI film on the surface of the lithium-free negative pole piece is low, and the effect of inhibiting the deposition of the transition metal ions on the surface of the lithium-free negative pole piece is not obvious; the high content of the transition metal element adversely affects the cycle life of the secondary battery. Alternatively, in the anode active material layer, the content of the transition metal element may be a range composed of any two numerical values in combination of: 10ppm, 20ppm, 50ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm or 850ppm. Further, in the anode active material layer, the content of the transition metal element is 20ppm to 500ppm or 20ppm to 200ppm.

In some of these embodiments, the transition metal salt comprises at least one of a nitrate, oxalate, sulfonate, acetate, and carbonate. Further, the transition metal salt is selected from at least one of nitrate, oxalate, sulfonate and acetate. Nitrate, oxalate, sulfonate, acetate and other transition metal salts have little influence on the electrochemical performance of the lithium-free negative pole piece.

In the lithium-free negative pole piece, the transition metal salt is mainly distributed on the surface of the negative active material layer far away from the negative current collector, so that an SEI film rich in transition metal ions is formed on the surface of the lithium-free negative pole piece. In some embodiments, the distribution depth of the transition metal salt is 10nm to 100nm in a direction from the surface of the negative active material layer away from the negative current collector to the negative current collector. Alternatively, the depth of distribution of the transition metal salt may be in a range consisting of any two of the following combinations of values: 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm. Furthermore, the distribution depth of the transition metal salt is 30 nm-80 nm.

In some of these embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material such as copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, or a silver alloy on a polymer material base material. The polymer material substrate includes substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

In some of these embodiments, the negative active material in the negative active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase micro carbon spheres, silicon-based materials, and tin-based materials.

In some of these embodiments, the negative active material layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some of these embodiments, the negative active material layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some of these embodiments, the negative electrode active material layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

Another embodiment of the present application further provides a method for preparing a lithium-free negative electrode plate, including the following steps:

the lithium-free electrode sheet is soaked in a solution containing a transition metal salt to allow the transition metal salt to penetrate into the negative electrode active material layer.

It can be understood that the lithium-free electrode plate is a conventional negative electrode plate. In some of these embodiments, the lithium-free electrode sheet described above may be prepared by: dispersing the components for preparing the lithium-free negative electrode plate, such as a negative active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the lithium-free electrode piece.

In some of these embodiments, the solvent of the solution is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl acetate, and tetrahydrofuran. Further, the solvent of the transition metal salt solution is dimethyl carbonate. The transition metal salt solution prepared by using the volatile solvents such as dimethyl carbonate and the like can be convenient for subsequent drying and solvent removal.

In some of these embodiments, the transition metal salt is present in the solution in an amount of 1% to 30% by weight. Alternatively, the mass percentage of the transition metal salt in the solution may be in a range consisting of any two of the following combinations of values: 1%, 2%, 4%, 5%, 6%, 8%, 10%, 15%, 20%, 25% or 30%. Further, the mass percent of the transition metal salt in the solution is 5-10%.

The content of the transition metal salt in the anode active material layer can be controlled by controlling the soaking time. In some embodiments, the soaking time is 15min to 180min.

The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

Negative pole piece

The negative pole piece adopts the lithium-free negative pole piece provided by the first aspect of the application or the lithium-free negative pole piece prepared by the preparation method of the second aspect.

Positive pole piece

The positive pole piece comprises a positive pole current collector and a positive pole active material layer arranged on at least one surface of the positive pole current collector, wherein the positive pole active material layer comprises a positive pole active material.

As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.

In some of the embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material such as aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, or a silver alloy on a polymer material base material. The polymer material substrate includes substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

In some embodiments, the positive active material may be a positive active material for a battery, which is well known in the art.

In some of these embodiments, the secondary battery further includes a positive electrode active material; the positive electrode active material contains a transition metal element. In some of these embodiments, the positive active material is selected from Li [ Ni ] _x Co _y N _z M _1-x-y-z ]O ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₃ ·(1-a)LiAO ₂ And LiFePO ₄ At least one of;

a is selected from one of Ni, co and Mn; a is more than 0 and less than 1.

As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates of olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxides (e.g., liNiO) ₂ ) Lithium manganese oxide (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some of these embodiments, the transition metal element in the positive active material is the same as the transition metal element of the lithium-free negative electrode sheet. When the transition metal element in the positive active material is the same as that of the lithium-free negative pole piece, the cycle life of the secondary battery is improved more remarkably.

In some of these embodiments, the positive active material layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.

In some of these embodiments, the positive active material layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some of these embodiments, the positive electrode sheet can be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

Electrolyte

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The kind of the electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

In some of these embodiments, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.

In some of these embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate phosphate, and lithium tetrafluorooxalate phosphate.

In some of these embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

In some of these embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

In some of the embodiments, the mass percentage of the additive in the electrolyte is 0.1% to 5%. Alternatively, the mass percentage of the additive may be in any range consisting of the following values: 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, or 5%. Further, the mass percent of the additive is 0.5-2%.

Isolation film

In some of the embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some of the embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some of these embodiments, the secondary battery may include an outer package. The exterior package may be used to enclose the electrode assembly and electrolyte.

In some of these embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 1 is a secondary battery 5 of a square structure as an example.

In some of these embodiments, referring to fig. 2, the overwrap may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed within the receiving cavity. The electrolyte wets the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.

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

Fig. 3 is a battery module 4 as an example. Referring to fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.

Fig. 4 and 5 are a battery pack 1 as an example. Referring to fig. 4 and 5, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides an electric installation, and electric installation includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The electric device may include, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, and the like. The mobile device may be, for example, a mobile phone, a notebook computer, or the like; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, or the like, but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to its use requirement.

Fig. 6 is an electric device 6 as an example. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the device may be a cell phone, a tablet, a laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Preparing an electrolyte:

to a non-aqueous organic solvent (EC: EMC =3: 7w%/W%) in a glove box filled with argon (water content < 10ppm, oxygen content < 1 ppm) was added 2wt% Vinylene Carbonate (VC) and after mixing was uniform, liPF was slowly added to the above solution ₆ To obtain a product containing 1mol/L LiPF ₆ The electrolyte of (1).

Preparing a positive pole piece:

the positive electrode active material, the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methyl pyrrolidone (NMP). LiNi _0.5 Co _0.2 Mn _0.3 O ₂ The mass ratio of Super P to PVDF is 95. Coating the positive electrode slurry on a current collector aluminum foil, drying at 85 ℃, cold-pressing, cutting edges, cutting pieces, slitting, and drying at 85 ℃ for 4 hours to obtain the positive electrode plate.

Preparing a negative pole piece:

and uniformly mixing the negative active material graphite with a conductive agent Super P, a thickening agent CMC and a binder Styrene Butadiene Rubber (SBR) in deionized water to prepare negative slurry. The mass ratio of graphite, super P, CMC and SBR is 94. And coating the negative electrode slurry on a current collector copper foil, drying at 85 ℃, then carrying out cold pressing, trimming, cutting and slitting, and drying for 12 hours at 120 ℃ under a vacuum condition to prepare a negative electrode plate. And (3) soaking the cold-pressed negative pole piece in a transition metal nitrate solution (the solvent is dimethyl carbonate) with the mass concentration of 10%, soaking for 15 min-3 h (the content of transition metal elements on the negative pole piece is adjusted by controlling the soaking time), and drying.

Specifically, the content of the transition metal element on the negative electrode sheet can be measured by the following method: pounding the same batch of current collector copper foils into a plurality of small wafers with the diameter of 12mm, weighing, calculating the average mass m1 of the copper foil small wafers, pounding the negative pole piece to be tested into a plurality of small wafers with the diameter of 12mm, weighing, calculating the average mass m2 of the negative pole piece, wherein m2-m1 is the mass of the negative active material layer, carrying out nitric acid hydrolysis on the whole negative pole piece, and carrying out an ICP-AES test (EPA 6010D-20143) to obtain the content of the transition metal elements on the negative active material layer.

Preparing a secondary battery:

a16 μm polyethylene film (PE) was used as a separator. And (3) sequentially laminating and winding the prepared positive plate, the prepared isolating membrane and the prepared negative plate to obtain a bare cell, welding a tab, placing the bare cell in an outer package, injecting the prepared electrolyte into the dried cell, and carrying out packaging, standing, formation, shaping, capacity test and the like to finish the preparation of the secondary battery.

Example 1:

in the secondary battery of example 1, the positive electrode active material was LiMn ₂ O ₄ The transition metal salt used in the preparation process of the negative pole piece is manganese nitrate, and the content of manganese element in the negative pole piece is 10ppm.

Examples 2 to 8:

examples 2 to 8 are different from example 1 in the content of manganese element in the negative electrode sheet.

Example 9:

in the secondary battery of example 9, the positive electrode active material was Li [ Ni ] _0.5 Co _0.2 Mn _0.3 ]O ₂ The transition metal salt used in the preparation process of the negative pole piece is manganese nitrate, and the content of manganese element in the negative pole piece is 100ppm.

Examples 10 to 16:

examples 10 to 16 are different from example 9 in the kind of transition metal salt.

Example 17:

in the secondary battery of example 17, the positive electrode active material was Li [ Ni ] _0.9 Co _0.1 Mn _0.1 ]O ₂ The transition metal salt used in the preparation process of the negative pole piece is nickel nitrate, and the content of manganese element in the negative pole piece is 110ppm.

Example 18:

the secondary battery of example 18, wherein the positive electrode active material was LiFePO ₄ The transition metal salt used in the preparation process of the negative pole piece is ferrous nitrate, and the content of manganese element in the negative pole piece is 120ppm.

Comparative example 1:

comparative example 1 is different from example 1 in that the negative electrode sheet does not contain a transition metal salt.

Comparative example 2:

comparative example 2 differs from example 9 in that the negative electrode sheet does not contain a transition metal salt.

Comparative example 3:

comparative example 3 differs from example 18 in that the negative electrode sheet does not contain a transition metal salt.

The kind and content of transition metal ions of the positive electrode active material and the negative electrode tab of the secondary batteries of examples 1 to 18 and comparative examples 1 to 3 are recorded in table 1.

Table 1 transition metal ion species and contents of the positive electrode active material and the lithium-free negative electrode sheet of the secondary batteries of examples 1 to 18 and comparative examples 1 to 3.

Test part:

secondary battery cycle performance test

The secondary battery was charged at 25 ℃ to 4.25V at a constant current of 0.5C (the charge cutoff voltage was 3.65V if the positive electrode was lithium iron phosphate), then charged at a constant voltage of 4.25V (3.65V for a lithium iron phosphate system) to a current of 0.05C, and then discharged at a constant current of 1C to 2.8V, which was a charge-discharge cycle. The capacity retention rate after 500 cycles of the secondary battery was calculated with the capacity of the first discharge as 100%. Capacity retention (%) after 500 cycles of the secondary battery = discharge capacity at 500 cycles/capacity at first discharge × 100%.

High-temperature storage life performance test of secondary battery

At 25 ℃, charging the secondary battery to 4.25V at a constant current of 0.5C, then charging the secondary battery at a constant voltage of 4.25V to a current of 0.05C, standing for 10min, then discharging the secondary battery at a constant current of 1C to 2.8V, recording the discharge capacity as D0, then placing the secondary battery into a constant temperature furnace at 60 ℃ for storage for 60 days, discharging the secondary battery out of the furnace, naturally cooling, when the surface temperature of the battery cell is recovered to 25 ℃, discharging the secondary battery at a constant current of 1C to 2.8V, standing for 10min, charging the secondary battery at a constant current of 0.5C to 4.25V, then charging the secondary battery at a constant voltage of 0.05C, standing for 10min, discharging the secondary battery for 2.8V, recording the discharge capacity as D1, and keeping the reversible capacity of the battery cell at a high-temperature storage life = D1/D0 x 100%.

The cycle performance and high-temperature storage life data of the secondary battery are recorded in table 2.

TABLE 2 cyclability and high-temperature storage life of secondary batteries of examples 1 to 18 and comparative examples 1 to 3

As can be seen from the data in table 2, the capacity retention rate of the secondary batteries of examples 1 to 18 after 500 cycles at room temperature (25 ℃) is 90.3% to 98.2%, and the reversible capacity retention rate at 60 ℃ storage life is 89.2% to 96.0%, and the secondary batteries of examples 1 to 18 have better cycle life and high-temperature storage life compared with the secondary batteries of the same system without the transition metal salt in the negative electrode plates of comparative examples 1 to 3.

In the secondary batteries of examples 1 to 8, the positive electrode active material was LiMn ₂ O ₄ The transition metal salt in the negative electrode plate is manganese nitrate, the content of the transition metal element in the negative electrode active material layer in examples 2 to 5 is 20ppm to 200ppm, the cycle life and the high temperature of the secondary batteryThe storage life performance is better.

In the secondary batteries of examples 9 to 16, the positive electrode active material was Li [ Ni ] _0.5 Co _0.2 Mn _0.3 ]O ₂ The transition metal elements dissolved out from the positive electrode active material are mainly Mn, co, and Ni, and a small amount thereof is also dissolved out. It can be seen from the data related to examples 9 to 12 that the transition metal salts in the negative electrode sheets of examples 9 to 12 are respectively manganese salt, nickel salt, cobalt salt and ferrous salt, and compared with the secondary batteries of examples 10 to 12, the transition metal element in the negative electrode sheet of example 9 is the same as the main dissolved transition metal element in the positive electrode active material, and the cycle performance and the high-temperature storage life performance of the secondary batteries are better than those of examples 10 to 12. The transition metal element of the negative electrode tab in example 12 is different from the transition metal element of the positive electrode active material, and the cycle performance and the high-temperature storage life performance of the secondary battery are slightly inferior to those of examples 9 to 11. The transition metal salts in the negative electrode sheets of examples 13 to 16 were sulfonate, oxalate, acetate and carbonate, respectively, and the cycle performance and high-temperature storage life performance of the secondary battery of example 16 using carbonate were superior to those of the secondary batteries of examples 13 to 15.

In the secondary battery of example 17, the positive electrode active material was Li [ Ni ] _0.9 Co _0.1 Mn _0.1 ]O ₂ The transition metal element dissolved out of the positive electrode active material is mainly Ni, the transition metal salt in the negative electrode plate is nickel salt, the capacity retention rate of the secondary battery of example 17 after 500 cycles at normal temperature (25 ℃) is 95.3%, the reversible capacity retention rate at 60 ℃ storage life is 94.7%, and the secondary battery has good cycle life and high-temperature storage life.

The secondary battery of example 18, wherein the positive electrode active material was LiFePO ₄ The transition metal salt in the negative electrode plate is ferrous nitrate, the capacity retention rate of the secondary battery of example 18 after 500 cycles at normal temperature (25 ℃) is 98.2%, the reversible capacity retention rate at 60 ℃ storage life is 96.0%, and the secondary battery has better cycle life and high-temperature storage life.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, so as to understand the technical solutions of the present application in detail and in detail, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. It should be understood that the technical solutions provided by the present application, which are obtained by logical analysis, reasoning or limited experiments, are within the scope of the appended claims. Therefore, the protection scope of the present patent application shall be subject to the content of the appended claims, and the description and the drawings shall be used for explaining the content of the claims.

Claims

1. A lithium-free negative electrode sheet, comprising:

a negative current collector; and

a negative active material layer disposed on a surface of the negative current collector; the negative active material layer includes a transition metal salt.

2. The lithium-free negative electrode tab of claim 1, wherein the transition metal element in the transition metal salt comprises at least one of Co, ni, mn, fe, cu, zn, cr, V, and Ti.

3. The lithium-free negative electrode sheet according to claim 2, wherein the content of the transition metal element in the negative active material layer is 10ppm to 850ppm;

4. The lithium-free negative electrode sheet of claim 1, wherein the transition metal salt comprises at least one of a nitrate, oxalate, sulfonate, acetate, and carbonate;

5. The lithium-free negative electrode sheet according to any one of claims 1 to 4, wherein the distribution depth of the transition metal salt is 10nm to 100nm in a direction from the surface of the negative active material layer away from the negative current collector toward the negative current collector;

6. The lithium-free negative electrode plate as claimed in any one of claims 1 to 4, wherein the negative active material in the negative active material layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon spheres, silicon-based materials and tin-based materials.

7. A preparation method of a lithium-free negative pole piece is characterized by comprising the following steps:

immersing the lithium-free electrode sheet in a solution containing a transition metal salt to allow the transition metal salt to penetrate into the negative electrode active material layer.

8. The method for preparing a lithium-free negative electrode plate of claim 7, wherein the transition metal element in the transition metal salt comprises at least one of Co, ni, mn, fe, cu, zn, cr, V and Ti.

9. The method for preparing the lithium-free negative electrode plate of claim 7, wherein the content of the transition metal element in the negative electrode active material layer is 10ppm to 850ppm;

10. The method for preparing the lithium-free negative electrode plate of claim 7, wherein the transition metal salt comprises at least one of nitrate, oxalate, sulfonate, acetate and carbonate;

11. The method for preparing the lithium-free negative electrode plate according to claim 7, wherein the distribution depth of the transition metal salt is 10nm to 100nm from the surface of the negative active material layer away from the negative current collector to the direction of the negative current collector;

12. The method for preparing a lithium-free negative electrode plate according to any one of claims 7 to 11, wherein the solvent of the solution is at least one selected from dimethyl carbonate, diethyl carbonate, ethyl acetate and tetrahydrofuran;

optionally, the solvent of the solution is dimethyl carbonate.

13. The method for preparing the lithium-free negative electrode plate according to any one of claims 7 to 11, wherein the mass percentage of the transition metal salt in the solution is 1 to 30 percent;

14. The preparation method of the lithium-free negative electrode plate according to any one of claims 7 to 11, wherein the soaking time is 15min to 180min.

15. A secondary battery, which is characterized by comprising the lithium-free negative pole piece of any one of claims 1 to 6 or the lithium-free negative pole piece prepared by the preparation method of the lithium-free negative pole piece of any one of claims 7 to 14.

16. The secondary battery according to claim 15, wherein the secondary battery further comprises a positive electrode active material; the positive electrode active material contains a transition metal element.

17. The secondary battery according to claim 15, wherein the positive electrode active material is selected from Li [ Ni [ ] _x Co _y N _z M _1-x-y-z ]O ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₃ ·(1-a)LiAO ₂ And LiFePO ₄ At least one of;

a is selected from one of Ni, co and Mn; a is more than 0 and less than 1.

18. The secondary battery of claim 16 or 17, wherein the transition metal element of the lithium-free negative electrode tab is the same as the transition metal element in the positive electrode active material.

19. The secondary battery according to any one of claims 15 to 17, wherein the secondary battery further comprises an electrolyte; the electrolyte comprises an additive;

20. The secondary battery according to claim 19, wherein the additive is present in the electrolyte in an amount of 0.1 to 5% by mass;

21. A battery module comprising the secondary battery according to any one of claims 15 to 20.

22. A battery pack comprising the battery module according to claim 21.

23. An electric device comprising at least one selected from the group consisting of the secondary battery according to any one of claims 15 to 20, the battery module according to claim 21, and the battery pack according to claim 22.