CN210576213U

CN210576213U - High-capacity high-rate lithium ion battery cathode

Info

Publication number: CN210576213U
Application number: CN201920880585.9U
Authority: CN
Inventors: 王永琛; 朱华君; 程凯; 王正伟
Original assignee: Phylion Battery Co Ltd
Current assignee: Phylion Battery Co Ltd
Priority date: 2019-06-12
Filing date: 2019-06-12
Publication date: 2020-05-19
Anticipated expiration: 2029-06-12

Abstract

The utility model discloses a high capacity high magnification lithium ion battery negative pole, including the negative pole mass flow body and the active material layer that is located the negative pole mass flow body surface, its characterized in that: and a black phosphorus coating layer covers the outer side of the active material layer. The utility model discloses a to material surface cladding phosphorus, the contact that has completely cut off silicon and electrolyte has restricted its volume expansion simultaneously, has increased electric conductivity, has avoided SEI to continuously grow and active lithium consumption, has improved the multiplying power performance and the circulation performance of silicon material.

Description

High-capacity high-rate lithium ion battery cathode

Technical Field

The invention relates to a lithium ion battery, in particular to a negative electrode of the lithium ion battery, and especially relates to a negative electrode for a high-capacity high-rate lithium ion battery.

Background

The negative electrode of the lithium ion battery is obtained by mixing a negative electrode active material, a binding agent and an additive to prepare slurry, uniformly coating the slurry on two sides of a negative electrode current collector and drying the slurry. The commonly used negative active material is a carbon material, such as graphite, but due to the problem of low specific capacity, the application of the negative active material in a high-capacity high-rate lithium ion battery (such as a power lithium ion battery) is restricted.

The theoretical gram capacity of silicon is 4200mAh/g (Li)_4.4Si) and graphite 372 mAh/g (LiC)₆) Silicon is the lithium ion battery negative electrode material with the highest specific capacity. But due to its large volume effect (>300%) and the silicon electrode material is pulverized and peeled off from the current collector in the charging and discharging processes, so that the active material and the active material, and the active material and the current collector lose electric contact, and simultaneously a new solid electrolyte layer SEI is continuously formed, and finally the electrochemical performance of the battery is deteriorated. In addition, pure silicon is a semiconductor material, and the rate performance is inferior to that of graphite due to very low intrinsic electronic conductivity, so that it is difficult to directly apply unmodified silicon to a lithium battery cathode. The Chinese patent application CN107093708A discloses a preparation method of an all-n-type silicon lithium ion battery cathode material, which comprises the steps of carrying out ball milling micron treatment and sand milling nano treatment on an n-type silicon material in sequence, cleaning the n-type silicon powder by using acetone and ultrapure water in sequence, carrying out surface oxidation treatment on the n-type silicon powder, mixing the oxidized silicon powder with a conductive agent and a binder to prepare cathode slurry, and preparing a cathode plate through coating, drying, tabletting and the like. The method treats the silicon to enable the silicon to be used for the negative electrode of the lithium battery, and simultaneously shows that n-type silicon has higher lithium storage capacity and rate capability than p-type silicon. But do not address the volume effectLeading to problems. In addition, as the circulation progresses, the silicon material gradually concentrates towards the surface of the negative plate away from the current collector.

The theoretical gram capacity of phosphorus is close to 2600mAh/g (Li)₃P) is 7 times that of graphite. The phosphorus is classified into white phosphorus, red phosphorus and black phosphorus, wherein the white phosphorus is toxic and has a low melting point, the red phosphorus is inflammable and slightly soluble in water, and the black phosphorus has good conductivity, the weakest reaction activity, the most stable property in the air and high density, so the black phosphorus is most suitable for the lithium ion battery. The unit cell of the black phosphorus is far larger than that of graphite, the distance between the formed lithium intercalation reaction channels is 0.43nm and is larger than 0.3354nm of the graphite, and the characteristic determines that lithium ions have high diffusion coefficient in the orthorhombic black phosphorus. Taking the phospholene material as an example, the diffusion rate of lithium ions therein is 100 to 10000 times faster than graphite. The electronic conductivity of the black phosphorus is up to 10²S/m is not less than 10 of graphite¹~10³And (5) S/m. In addition, since the lithium intercalation potential of phosphorus is 0.8V, which is higher than that of silicon, the density of phosphorus is 2.69g/cm³Higher than 2.33 g/cm for silicon³Therefore, the black phosphorus is very suitable for the lithium battery negative electrode material. However, phosphorus has a volume effect as silicon, and the lithium intercalation potential of phosphorus is too high, which results in a lower battery voltage, so that pure phosphorus is not optimal as a negative electrode material.

In the prior art, phosphorus is usually applied by doping, for example, chinese patent application CN107240693A discloses a phosphorus-doped silicon-graphite composite material, which contains phosphorus-doped n-type silicon and graphite. During preparation, a mixture I containing silicon and phosphorus is subjected to ball milling in a protective gas atmosphere to obtain a precursor, and a mixture II containing the precursor and graphite powder is subjected to ball milling in the protective gas atmosphere to obtain the phosphorus-doped silicon-graphite composite material. For another example, chinese patent application CN107482173A discloses a negative active material of a lithium ion battery, which comprises a composite formed by connecting a carbon material and black phosphorus through a C — P bond. According to the technical scheme, the negative electrode material is obtained through doping, the problem of volume expansion can be restrained to a certain extent, the problem of volume expansion still exists, and the phenomenon that the silicon material slowly moves to the surface of the negative electrode plate in the battery circulation process cannot be solved.

Disclosure of Invention

The utility model aims at providing a high capacity high rate lithium ion battery negative pole, through structural improvement, the volume expansion of restriction silicon material increases the electric conductivity, makes it be applicable to high capacity high rate lithium ion battery.

In order to achieve the purpose of the invention, the technical scheme adopted by the utility model is as follows: the high-capacity high-magnification lithium ion battery negative electrode comprises a negative electrode current collector and an active material layer positioned on the surface of the negative electrode current collector, wherein a black phosphorus coating layer covers the outer side of active material particles.

Preferably, the thickness of the black phosphorus coating layer is 1-10 nm, and more preferably 2-5 nm.

Preferably, the active material layer is a silicon or silicon-oxygen-black phosphorus-carbon mixed layer, and the thickness of the active material layer is 50-150 μm, and more preferably 120-140 μm.

Preferably, the thickness of the negative electrode current collector is 4-12 μm, and more preferably 6-8 μm.

In the above technical solution, the active material layer contains one or more of black phosphorus, carbon, and silicon monoxide in addition to silicon. The total mass of the black phosphorus in the coating layer and the active material layer is 2.2-22% of the mass of silicon.

The theoretical gram capacity of silicon in the fully lithium-intercalated state is 4200mAh/g (Li)_4.4Si), the theoretical gram capacity of phosphorus is 2596mAh/g (Li)₃P). When a lithium ion battery is first formed, most of the lithium salt is consumed to form a negative solid electrolyte interface film SEI. Lithium is an acceptor material, a material phosphorus is applied to a coating layer on the surface of the silicon cathode, a formed SEI film can have electric neutrality, and meanwhile, strong bonds between the phosphorus and the silicon can tend to be alloyed, so that the influence of an electric field on carriers in the silicon body is effectively weakened.

Si is a tetravalent element, Li is a monovalent element, and P is a pentavalent element, so 1 mole of Li_4.4With 0.4 mol of lithium in Si, 1 mol of Li, possibly forming acceptor impurities₃Also 2 moles of lithium are required in P to form a neutral species. The current optimal first coulombic efficiency for silicon based materials is 90%, so 10% of silicon is considered for the first loss under the limiting conditions. Of substances requiring an outer coating of phosphorusQuantity n_pAmount n of substance being silicon_si0.1 x 0.4/2=0.02 times. Since the atomic weight of phosphorus is 31 and the atomic weight of silicon is 28, the lower limit mass of phosphorus coated on the silicon surface is 0.02/28 × 31=2.2% of the silicon mass. When silicon is used in the negative electrode of a lithium ion battery in a state where a complete lithium intercalation occurs, the state is Li_4.4Si, so the amount n of phosphorus species required_pAmount n of substance being silicon_si0.4/2=0.2 times. Since the atomic weight of phosphorus is 31 and the atomic weight of silicon is 28, the upper limit mass of phosphorus coated on the silicon surface is 0.2/28 × 31=22% of the silicon mass.

Except that the black phosphorus in the coating layer forms the surface coating by a vapor deposition method, a spraying method, a hydrothermal method or a sol-gel method, the other black phosphorus realizes the bulk doping of silicon in the active material layer by a thermal diffusion, injection or mixing method.

In the above technical solution, the active material layer includes one or more of a nano silicon material, a porous silicon material, a hollow silicon material, a silicon-carbon composite material, and a silicon-oxygen composite material. Wherein the active material layer may be doped with black phosphorus.

According to the technical scheme, the silicon surface is coated with the black phosphorus, so that the contact between the silicon and the electrolyte is isolated, and the continuous growth of an SEI (solid electrolyte interface) film and the consumption of active lithium are avoided. Meanwhile, the coated black phosphorus tends to have the structural characteristics of phospholene, so that the volume expansion of silicon can be limited to a certain extent. The contact internal resistance among active material particles can be reduced by utilizing the high conductivity characteristic of the black phosphorus on the surface, and the multiplying power of the battery is improved. It is worth noting that the black phosphorus of the coating layer can solve the phenomenon that the silicon material slowly moves to the surface of the negative plate in the battery cycle process.

Because of the application of the technical scheme, compared with the prior art, the utility model has the following advantages:

1. the utility model discloses a set up the black phosphorus coating, completely cut off the contact of silicon with electrolyte, the black phosphorus of coating tends to have the structural feature of phosphorus alkene, can restrain the volume change of silicon, can also effectively completely cut off the contact of silicon and electrode liquid, avoids SEI to continuously grow and active lithium consumption.

2. In the utility model, the black phosphorus on the surface has high conductivity, which can reduce the contact internal resistance among active material particles; the doped phosphorus in the silicon enables the silicon to form an n-type electronic conductive semiconductor, improves the conductivity of the silicon material, has high diffusion performance, and finally improves the rate capability of the silicon material.

3. The utility model discloses a phenomenon that silicon material slowly moved to the negative pole piece surface in battery cycle process can be solved in the setting of coating, finally greatly improves the cyclicity performance of silicon system material.

4. The utility model provides a reasonable phosphorus content slightly reduces the theoretical gram capacity of negative pole, finally makes silicon have high reversible capacity.

5. Compared with the traditional graphite cathode, the utility model has the characteristic of high capacity; compared with a pure silicon system cathode, the utility model has the characteristics of high multiplying power and long cycle life.

Drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention;

fig. 2 shows a cell test cycle according to an embodiment of the present invention;

fig. 3 is a result of the cell normal temperature 2C rate charge test of the embodiment.

1. A negative current collector; 2. an active material layer; 3. a coating layer; 4. a silicon-based material body.

Detailed Description

The invention will be further described with reference to the following examples:

the first embodiment is as follows:

referring to the attached drawing 1, the high-capacity high-rate lithium ion battery cathode comprises a cathode current collector 1 and an active material layer 2 positioned on the surface of the cathode current collector 1, wherein the main body in the active material layer 2 is a phosphorus-containing silicon material, the outer side of the material is covered with a black phosphorus coating layer 3, and the material is internally provided with a silicon material body 4.

The preparation method comprises the following steps: mixing silicon containing phosphorus, graphite, a conductive agent and a binder, coating the mixture on two sides of a current collector, and then drying and compacting to prepare the pole piece. Phosphorus is prepared by vapor deposition, spraying, and waterAnd forming a coating layer on the silicon surface by a thermal method or a sol-gel method, wherein the mass of black phosphorus of the coating layer is 2.2% of that of the silicon material. The main active substance is silicon containing phosphorus, the mass of the silicon containing phosphorus accounts for 10% of the mass of all solid substances, the mass of graphite accounts for 85%, and the mass of the other auxiliary materials, namely the conductive agent and the binder account for 5%. The density of the coated double-sided surface is 220g/m²The current collector is a 6-micron copper foil, the compacted density of the pole pieces is 1.7g/cm3, the thickness of the pole pieces is 130 microns, the size of the negative pole piece is 80 x 143mm, the number of the negative pole pieces is 80, the same 622 ternary system positive pole pieces are matched to assemble a 50Ah square aluminum shell monomer battery cell, and the energy density is up to 250Wh/kg (the model of the square battery cell is 2614891). And testing the normal-temperature 1C charge-discharge cycle life, the 2C constant-current charge ratio and the 2C charge temperature rise of the battery under the same conditions.

And (3) testing the cycle conditions (the cycle step is that 1C constant current charging is carried out to 4.2V, constant voltage charging is carried out to 0.05C, the time is 0.5h, 1C constant current discharging is carried out to 2.7V, and the time is 0.5 h.) under the condition of 25 +/-2 ℃), wherein as shown in figure 2, the cycle life of the ordinary n-type silicon material cell is 1000 times, the cycle life of the n-type silicon material cell coated with 3nm phosphorus can reach 1500-1600 times, and is improved by 50% compared with the ordinary n-type silicon material cell.

The normal temperature 2℃ rate charging test (test procedure: 2℃ constant current charging to 4.2V at 25 ± 2 ℃ and constant voltage charging to 0.05℃) was carried out, and as shown in fig. 3, the constant current charging ratio of the ordinary n-type silicon material cell was 87.25% while the temperature rise was 12.3 ℃, whereas the constant current charging ratio of the 3nm phosphorus-coated n-type silicon material cell was 88.81% and the temperature rise was only 8.7 ℃. A higher constant current charge ratio means less polarization of the cell, and a lower temperature rise means less heat generation. In conclusion, the cell performance of the n-type silicon material coated with 3nm of phosphorus is superior to that of the cell of the common n-type silicon material.

Claims

1. The utility model provides a high capacity high magnification lithium ion battery negative pole, includes the mass flow body of negative pole and is located the active material layer on the mass flow body surface of negative pole, its characterized in that: and the outer side of the active material particles is covered with a black phosphorus coating layer.

2. The high capacity high rate lithium ion battery negative electrode of claim 1, wherein: the thickness of the black phosphorus coating layer is 1-10 nm.

3. The high capacity high rate lithium ion battery negative electrode of claim 2, wherein: the thickness of the black phosphorus coating layer is 2-5 nm.

4. The high capacity high rate lithium ion battery negative electrode of claim 1, wherein: the thickness of the active material layer is 50-150 μm.

5. The high capacity high rate lithium ion battery negative electrode of claim 1, wherein: the thickness of the active material layer is 120-140 μm.

6. The high capacity high rate lithium ion battery negative electrode of claim 1, wherein: the thickness of the negative current collector is 4-12 mu m.

7. The high capacity high rate lithium ion battery negative electrode of claim 1, wherein: the thickness of the negative current collector is 6-8 mu m.